I wish to change from the marriage visa to a retirement one, I am over 50 and have had over 800,000 baht in the bank here for all of this year. What other documents do I need to take to immigration other than passport and bank book and letter from bank? Also is it better to apply when I must report for the 90 days next month or wait till the existing visa runs out in December? Thanks for your help.

Wait until around 30 days before your current extension expires. (Note Extension not Visa)

As you said, letter from bank, up to date passbook, passport, passport size photo.

Thanks for replying, so no medical certificate or condo ownership proof required?

No medical cert needed.

Reports suggest you will get the extension while you wait,

not a month later as with marriage.