It used to be possible to get a retirement visa, under 50, if on medical grounds, from outside Thailand, but it couldn't be extended, so not ideal... I did it once, then went for the Elite visa
You can get a non o, or just come on visa exemption and convert to non o here, easiest if using an agent, to do that.. Better to get non o, so you don't need an agent to help open a bank account
Then get an extension based on marriage or retirement.
Married extensions only need 400,000 baht in an account, but they need a lot more paperwork proving that you are still living together... Retirement extensions are easier.