You've got the Non-O Retirement visa. You used it to enter. Deposit the money in your Thai bank. Season it then apply for 12 month extension of stay at immigration office. They will have a list of paperwork required.
I send money via wise direct to Thai bank. So get the visa before you arrive. Enter Thailand. Open bank account. Transfer money direct to account. Apply for 12 months extension of stay.
Non-OA needs insurance from a limited choice of companies with less than favourable cover. The visa is only valid for the same duration dates of the insurance. Non-O you can buy whatever insurance you prefer.
visas haven't changed. The entry with "no visa/visa exempt" has been tightened up. Apply for a visa before you arrive would be the best thing to avoid issues.