In (very) short non-o Retirement visa is more money in the bank, less paperwork, compared to the marriage visa. Regarding your certificate of residence to open a bank account, they are only valid for 30 days from issue and the reason for issue, needs to be to open a bank account. You might be better off looking at the non-oa requirements.
You'd get a 30 day extension in your local immigration office. Ranong - Myannmar by boat is the closest border point, if you just want to bounce in and out, not a Visa run, for another 60 days. It was open last time I checked but that may have changed.