Is 90 days enough to apply for a retirement visa in Thailand after extending my 60 day exemption?

Do you already have a Thai bank account for the 800k international transfer?

Go to your immigration office file for a 30 day extension on your 60 day visa exempt entry stamp for 1900baht.

Then get the hand out from them listing the requirements to get the 90 day Non-O visa based on retirement.

You need a minimum of 15 days left on your current stamp to apply for that at most immigration offices <- that means you need to get the 800K baht transferred into a thai bank account in your name only so you can get the process going and apply for the visa at the immigration office for 2000baht before you run out of time