Non O can be applied for with minimum 15 days remaining on permission of stay from visa exempt entry.
Note some offices require longer
CM 21, Phuket 15 working days etc
Do you have a Thai bank account in your name only.
Process outlined here
https://aseannow.com/topic/1311886-visa-exempt-to-retirement-extension-process-and-cost/
Note: Jomitien were asking for 800k in bank for 2 months prior to application for non O.
The actual rule is 800k on day of application (no seasoning)