Just an update for future reference to whoever might need it.
Documents I submitted to the Immigration:
Form TM6 filled in and with photo attached
Copies of relevant passport pages (ID page and all the extension pages)
Account statement bank letter (1 day old)
Copy of updated bankbook (updated on the application day)
Hand drawn map to my house (the same I submitted for married extensions)
Copy of wife's Tabien Baan
Copy of our marriage certificate
The last item, I was told, was needed because I changed from married to retired extension. Would not be needed next time. The IO doing my application asked if my wife was there, and called her to sit with me, but didn't ask her anything, or to sign anything. For all that mattered it could have been my Mia Noi.....
The only question that came up was why the bank account started in April. I replied that I've cancelled the old account I used for married extension and started a new one. Also, I keep 1 million in the fixed account. Seem to be liked by IO's and avoids any problems with proving your financial status. It's also good to have 200K baht as an emergency fund, if need arises.
All items need to be verified against the originals. Lucky me having marriage certificate copies and the original.
All in all it took about 15 minutes from seeing the IO to getting the passport back with the stamps. They also updated my 90 day reporting. This might be because I just got back from Europe 2 weeks prior.