You do not make enough pension to get a yearly extension of stay based on monthly income alone. You need at LEAST 65K baht a month and you say you have 700K baht a year <- which is
*****
a month.
You would need to either bank 800K baht in a thai bank account in your name only OR you would need to bank the difference between your pension 700K baht a year and 800K baht <- so you would have to bank at least 100K baht to get a Non-O visa/extension based on being over 50