I’ve lived in the UK and in Aus, both for many years and as a child and an adult.
Firstly, it would depend on where in Australia you would like to live - Perth is very isolated but has a mild winter and scorching summer, some areas of NSW, SA and Vic get weather comparable to the UK but not as cold, however wet and windy with summers being much nicer/hotter than UK but not really as hot as Perth gets on a consistent basis. Darwin is lovely but the mosquitoes are crazy AF and along with Cairns and FNQ, very humid. Tasmania is, I think, the closest to the UK. The problem is this: no one is able to give a definitive answer as the states are all large and the weather varies according to where you are. You say you want an outdoor lifestyle, well, in the summertime, not many places (Tasmania however is the outlier) are able to facilitate that, because of either the heat, humidity or UV ratings that day. And no, a hat doesn’t really cut it and SPF50 is absolutely essential, especially if you’re blue eyed, with fair skin, and fair hair or ginger hair. Even Indians need SPF50.
The COL thing: wages are much, much higher than the UK and so is the standard of living. Yes, groceries may cost more depending on what you buy but there are plenty of places to shop that sell locally produced products. Housing costs depend on the state and where you want to live. Car costs vary wildly, depending on whether you want a little Hyundai for $25K (new) or an SUV (very expensive new and secondhand) or a brand such as Tesla, Mercedes, BMW etc.
If you’re under 30, I believe you can go to Aus on a WHV for one year, with an extension for another year.
Alternatively, there are lovely little islands in Oceania if you would prefer an island lifestyle and are eligible for a visa - Micronesia, Polynesia and Melanesia (which sounds like a skin disease but isn’t lol).