Do not add her to the account your visa money is in. That would void the use of that account for your visa unless you always have more than double of the requirement (as you then only own 50%). You can have other accounts that are joint. Marriage visa is not a requirement for that, and you should be able to do that with proper documentation (including marriage certificate).
I opened a joint savings account with my wife in Kasikorn doing that.
if it's a retirement visa/extension it is irrelevant if you are married or not. For that it is 800K/65K. For a marriage visa/extension it's irrelevant if you are retired or not. For that it is 400K/40K.
well.. There might be a few. But in order to use those, you would need to live in their area. As you probably know, for this extension you need to provide rental contract (if applicable) or blue book if not (your wife's house) plus providing photos of you living in the space. Plus an almost certain to happen home visit from immigration, for at least the first application in that area. You can't just shop around, going to a hotel in the area to get a tm30, for that office to process the extension. You need to actually live there, and be able to prove it. So if your luck, just as mine, means the office that service your area won't accept international transfers alone (like most of them), then you need to think long and hard about that 😂
I think that holds true for most immigration offices here. For monthly income option, it either has to be verified by your embassy, or be a verified Thai income. Only other option is the 400K banked.
Myself being on my 8th (soon 9th) consecutive extension like that.
You can apply for medical insurance at any time, from anywhere. As the non o has no requirement about insurance, it is not connected to your visa at all. Start to shop around and find the one you want.