that isn’t the point. You must buy one of the approved Thai policies. They will not accept better policies with overseas companies. The Thai policies are generally more expensive for worse cover. People that already have excellent cover have been forced to buy another policy to get an Extension. Also, older people can’t actually buy a new Thai policy anyway.
Initially: Non O gives 90 days, Non O-A one year. At the moment, both require insurance if you get in the U.K. Both visas can then be used to get Annual Extensions of Stay. Both require 800k in Thai bank to get Extension of Stay. Both require 90 day reporting. O-A requires Thai Health insurance for Extension, Non O does not require insurance for Extension.
So, initially, the O-A gives you longer but if you plan to stay in Thailand long term then the Non O does not require you to buy a Thai Health Insurance policy.
There’s no specific amount in the U.K. account to get a Non O for marriage/family, you just need to show some funds. They’re not too strict.
You don’t need any money in a Thai bank to get the visa but if you end up getting an annual extension in Thailand you’ll need at least 400k baht in your Thai account for at least a couple of months before.
in the U.K. they will give a CofE to someone with a valid Non O ‘retirement’ visa or extension IF they also have a Thai wife or child. Hopefully, it’s the same in Oz then you don’t need to change your visa.