Thank you everyone for your helpful comments. Currently we spend 4,000 pounds/month in London excluding rent/mortgage. We paid up for our house luckily, so have no mortgage. Things have shot up considerably recently and our costs have gone up at least 1K/month in the last year or so (and our lifestyle has not changed at all). The only thing that changed is we now have private health insurance after waiting for months for NHS treatments and never getting it. Our health insurance does not cover dental and optician, but we don't have to pay anything out of pocket for hospital treatment/consultant fees. Even under NHS, we always had to pay for dental costs. It's only free if you are on low income or under 18. And we also pay for glasses and for optician appointments (these things are not covered by NHS anymore unless you are a child/elderly/low income/special health conditions). At least this is the case in London. Last month our utility was £160 despite having solar and batteries as heating is by gas (this is after being stingy with heating and using it as sparingly as we can). Gone are the days when we could keep the heating on all day and it would be £70-80.
My four siblings live in Sydney. One with kids same age as mine says he spends 6,000 aud per month including mortgage. This seems to be on the low side comparing to what I am hearing on this forum. He lives a good lifestyle (not lavish, but same as me in London). He doesn't have private health insurance and he said healthcare is fine. He is in a similar career to me and earns 30K more (with similar experience level).
My parents don't have health insurance, my mum had a sudden heart issue a few months ago for which she had to be hospitalised for 2 weeks and the care was absolutely topnotch (I went over to for 2 weeks to look after her). Had all her procedures done swiftly, nurses and doctors always had a smile on their faces. Did not pay a penny. Compared to the NHS, service and facilities were AMAZING. Dare I say, it was even better than the private hospital facilities I experienced here when I had a surgery last year. I probably won't go for health insurance there just yet (might reconsider when I am older and really need it). The veg and fruits were so much better there, even the meat and fish seemed more fresh. All these things are making us consider moving back to sydney.
Re house, I do feel they are par London, but you get a much bigger living space there. But Sydney is a large place, so prices vary greatly. Where my family lives, there are brand new decent 4 bed houses for sale for circa 1.3 million aud (sydney south west). I know it's not a great place to live in sydney standard, but feels much nicer, safer and cheaper than London. Maybe I am just thinking the grass is greener on the other side. I go home every 2 years but never really felt the pull to move back so strongly until now. With the rising costs, London has very little to offer now. I can't see how my kids will ever afford to buy a place here with the meagre salaries they offer.