As
@Robert ******
said...
Ask your local Thai immigration office for their requirements for the Non O Visa as retiree and the One year extension of stay as retired ... and if they will accept your funds placed in Sterling.
IF you both enter Thailand with a tourist visa...you will EACH need 800,000 Thai baht in a Thai bank account to obtain the Non O Visa as retiree. Total of 1.6 Million Thai baht.
IF you obtain the Non O Visa as retiree outside of Thailand you will only need 800,000 Thai baht in ONE Bank account with the spouse issued as a trailing spouse.
OR if difficult to obtain the Non O Visa where you now are ..
Enter Thailand EACH with a tourist visa...and go to a neighbor SE Asia country and obtain the Non O Visa as retiree.