Probably not the best time to go there as it's middle of winter?!

Presumably they've thought of that & this is the only time to go. It will be warm in Cairns etc I would have thought?

Cairns will be warm, most of Oz will be springlike to Europeans, unless you were going to Tassie.

Every hotel in Cairns will have a pick up for a trip to the barrier reef, check what you want as some are more generic trip to a Cay, quick dive if you are interested and a semi submersible.

The rainforest is a must.

For Singapore, I'd do the stopover on the way back purely due to flight times. On the way out it is 12 hours to Singapore than a short hop to Australia (relatively short anyway). I'd recommend sticking your smining stuff in your hand luggage and using the pool in the Airport between flights.

Then on the way back you will be more awake and relaxed than after a 12 hour flight and closer to right time zone.

Also there are things you might like to buy that you can't take into Australia, things made of wood have to be declared and tested going into Australia but not to bring into Britain and the same for some food stuffs (obviously check).

One last thought, sometimes round the world tickets are the same or not much more than returns to Oz.

We went end of July / beginning of August. A week in Sydney...it was quite cold there, like our Autumn. We had a week on Lizard Island on the Great Barrier Reef where the weather was gorgeous. Some people were snorkelling in wetsuits etc as they thought it was cold, but to me it was perfect.
We then did a week on the Great Ocean Road out of Melbourne, but that was wintry. Rain and wind every day. Back to Sydney then and nice dry crisp days.

Personally I would wait to see what happens with all the bushfires ...they’re predicting that they will go on for another couple of months at least.

Are you desperate for a stopover both ways? Best to get the journey over and done with ime.

My overriding memory of Sydney in July is it being freezing, mostly because my family members in Australia don't seem to believe in heating their houses!

I second Lizard Island. Please don’t go with one of the mass produced barrier reef tours. They boats go to the same pods daily with hundred of tourists so all the coral and most of the fish have died off.

Well who wants to go at this time of year with 40 degree plus heat and fires? July and August are now great times to go. Heat isn’t everything on a holiday!

Sorry: the airline you use will determine the stop over.

We went in August 2 years ago and had a lovely time and an amazing holiday, around Cairns was around 27C which was perfect temp for us.

It's a great time to see Great Barrier Reef - daughter went scuba diving and we went snorkelling and saw reef and giant turtles. We also saw loads of wildlife, stayed at a place where lady looks after injured wildlife - Lumholtz lodge and there were tree kangaroos, possums, pademelon, bettong etc, she also told us where to find platypus which we saw. Stayed in a treehouse in the rainforest - again wildlife there possums and pademelon and wallabies which kids loved. Saw Daintree rainforest and crocodiles in the river. Didn't get to Magnetic Island but would have loved too, that has wild koalas on.

We also went as BA flights go via Sidney for couple of days in Port Stephens - went whale watching - was 22C and sunny that day which locals seem to think was freezing and needing of coats but same as English summer day and we saw hundreds of whales and some dolphins. Didn't see any koalas in wild there but locals so friendly. In Sydney weather was around 14C and windy but as flying via there went anyway - had breakfast with koala at featherdale and saw bridge and Blue Mountains where it was 10C but we saw wild kangaroos. So if you are going for wildlife rather than a holiday in the heat with beaches its fine. 27C was plenty warm enough for us and with our school holidays its quite restricted - our Christmas would be far too hot for us and Easter is not so good for Great Barrier Reef so for us our summer was best option. We prefer temps around 25C to 30C, any hotter and the kids and I really struggle.

We did GBR with Seastar in Cairns which was recommended to us by locals on Tripadviser forum, was very good, small boats, saw giant turtles. They recommended a couple in Port Douglas and said Port Douglas was a nicer place to stay. It was but was also much more expensive. I got excellent advice on Tripadviser Australia forum of best places to stay - they completely rearranged my original plans but very glad they did.

Wed like to go and stop in Singapore one way and just be in transit in singapore airport (and doze and swim!) the other. Singapore airlines really are the best!

Following for ideas.

Singapore is a great stop off point, we spent a week there recently and I can’t wait to go back.
Kuranda walks and market.
Rainforest. Cairns is great as is port Douglas but Port Douglas is expensive and a bit restricted as to what you can do there,

As one poster said, the airline you use will determine the stop over location and it’s generally cheaper to get a return trip on one airline than two single trips by different airlines, so it will likely be the same stopover location each way.

It’s a good time of year to go to Cairns as there’s no stingers that time of year so you don’t have to worry about wearing stinger suits or staying in netted areas.

Singapore airport is pretty interesting in itself, lots of detail on their website.

We much preferred Port Douglas to Cairns. The weather was lovely in June/July when we were there.
Sydney was rainy and cool, but fine.
Yes to the rain forrest.

I think you will struggle to find sensible priced flights stopping in different locations in each direction. Maybe just try pricing up a double Singapore stop vs a Singapore and a "somewhere else" flight.
Bangkok and KL are the other 2 that spring to mind.

Well who wants to go at this time of year with 40 degree plus heat and fires?

Just returned from WA. 19 degrees when I left and raining. A few fires but nothing remotely similar to those over in the eastern states.

August is perfect for Cairns probably the best month to go weather wise (lived there for 10 years) Personally I would stay in Cairns and hire a car to see the rainforest and waterfalls in the Atherton Tablelands, go to Cape Tribulation via Port Douglas on the way. I would also try and take a river cruise at Cape Trib to see wild crocs on the river. Head out to see the reef, take skyrail and train to Kuranda, white water rafting, sky diving .......have a great time!

we're going to NZ at the same time as OP (fitting in a decent length of trip before exam results is tricky, I agree), and we're doing a round the world (UK-San Francisco-NZ; NZ-Singapore-UK) booked with Air New Zealand, but the legs are mostly codeshares, so we'll have three different airlines in total. We decided in the end not to bother with proper stopovers, and just to get the flights over and done with, so as to get the most time we could in NZ (and even then, we can only do a fraction of the things on our Want To See lists).

I am regretting not booking the Emirates flights I saw for £650 each return though, two weeks later they were at £3k .

I'm a firm believer in not stopping over - you end up with two lts of jet lag! Get there in one go, stay up as late as you can, take some melatonin or a sleeping tablet for the frist couple of days.

I'm a firm believer in not stopping over - you end up with two lts of jet lag!

It depends where you are going. Singapore and Perth are in the same time zone.

We did BA multi-flight which was £1100 per adult London- Sydney - Cairns and back - Quantas for Cairns flight. Weirdly BA multi flight charged same for one flight as two on some dates. Singapore Airlines you can go via Singapore to Cairns so less flying but you miss Sydney which I wanted to see as might be our only trip there. £650 was a bargain. I looked at Virgin and they were £3k each Probably worth using Skyscanner to find best options.

In Cairns we stayed in an AirBNB Billabong B&B but can't see it on there now - seems to be on other sites, around £100 per night for 4 of us, had apartment and there was a lake / billabong you could canoe on and tropical gardens, lovely and great value. Needs hire car. Then Lumholtz Lodge and Canopy Treehouses - both great for wildlife, about £200 a night each and at Lumholtz we had full board which was amazing homecooked foods with wine. Owner was German. Canopy Treehouses has no wifi though which kids didn't like but did have rainforest, treehouse, possum, pademelon, wallabies and cassowary on site.