Can I extend my OA visa for another 12 months upon re-entering Thailand with a new health insurance certificate?

@Matt ******

Matt Doran you do not need to present a financial proof going into the "second" year of a Non-O/A visa

However if you plan to apply for the "1-year Extension of Stay" based on retirement near the end of your “second year”, you will need either a proof of 800.000.- THB in your bank account, seasoned for two months on the day of your application, or a bank statement that proves you have transferred from abroad a minimum of 65.000.- THB for 12 consecutive months, month for month.

And with the application to the 1-year Extension from out of a former Non-O/A visa, your foreign health insurance will not be accepted any more by Immigration. You will need a yearly Thai private health insurance, contracted with one of those Thai insurance companies that are listed on the "tgia-list of insurances"

"If I go with the 65,000 per month for my second year - do I still need a minimum balance of 400,000 baht for that year?" . . . . . . you DON'T NEED a financial proof for the "second year" out of a former Non-Imm-O/A visa. You will only need the financial proof when you apply for the 1-year Extension of Stay Permit

@Matt ******

Okay, the answer to your question (which you asked twice) is YES

You need to meet the seasoning requirements of the extension you're on NOW which you got by banked money, <- which means you need to keep the 800K baht in the account for 3 months after the extension was granted

AND

you then can't let the balance go below 400K the rest of the year (until you apply for the following year's extension)

ALSO

You have to transfer in to the country from abroad a minimum of 65K baht a month, each month every month for the previous 12 months before you apply for the new yearly extension based on monthly income method