As others have said, look for ways you could try out living there - such as a job share - without having to commit to a permanent move. And think carefully and honestly about how you enjoy spending your time. Will Oz offer you what you are looking for?
I worked in Oz for a year. Loved my time there but still opted to come back to the UK rather than extend my contract.
On the plus side:
Sunshine obviously - particularly the predictability of the weather. You know that, if you plan a picnic for Saturday, there is a 99% chance of it being fine. Also, it is sunnier in the winter, even in colder cities like Melbourne, so you don't mind winter so much
Friendliness
General informality
Very varied scenery & lots to do outdoors.
Mood of optimism
On the downside:
Sunshine: it is too frigging hot to be active outdoors much of the year. At 5 am, the beaches are packed with walkers & runners because it is too hot to go later.
Although friendly, lots of Australians have gone to school, uni & settled down in the same town. Groups of friends go back decades and it may be hard to break in.
Though less formal than the UK at work, they can be surprisingly bureaucratic and humourless. Australians take themselves quite seriously. You will be expected to take a lot of teasing about "whinging Poms" with a smile, but they won't find it funny if you take the piss back.
They are generally pretty inclusive towards immigrants (whinging Pom gags aside), but the levels of open racism towards aboriginal peoples are shocking. There is also a very macho culture.
You will be starting again. You'll keep in touch with friends and family back in the UK, but realistically, there are many you will never see again.
Yes, there is lots to do outdoors but there is nothing to do on a wet Wednesday. Even in Sydney & Melbourne, you could visit every museum & cultural centre in a day. Western Oz is 4-5 hours from much of Asia, but the east coast is a very long way from the rest of the world (apart from NZ which doesn't count as no Australians seem to go there).