I emigrated from the UK to NZ and lived there for almost 20 years before moving to Australia. Depending where you go, climate can be much better in either country than the UK; Australia can get really hot though - air temps of 40 or even 50 degrees, ground temperatures literally reaching the 80s outside my apartment in summer. It's a bit much for me tbh.
IT is relatively well paid in both countries and cybersecurity skills are in demand. Costs seem a bit higher than the UK, but you'll likely feel that you have a better quality of life over here. I work in the same field, for a cyber company with offices across both countries, so feel free to contact me if you make the jump.
NZ feels a bit more laid back which I preferred. Australia has much better healthcare though, better salaries generally, better worker's rights. Probably better education too - NZ seems on a downward spiral there. Bigger population in Australia, so more of the big cultural stuff happening. Housing is an issue in both countries, but that IT salary will help.
If you get citizenship in either country, they have reciprocal rights, so moving between them is easy. As others have said, it's a long, long way back to the UK - almost 4 hours from NZ to Australia, and then another 4 hours across Australia before you even leave the country!