@Gary *******
Your roadmap should be:
1. Apply for the 90-days single entry Non Immigrant O retirement/over 50 visa BEFORE you travel to Thailand.
2. get a 90-days stay permit stamped upon entering Thailand
3. Visit your local Immigration Office for a Certificate of Residence and the hand out to apply for the 1 year Extension of Stay.
4. Visit a bank branch with passport and documents from point 3 and open a bank account, so you can deposit a minimum of 800.000 THB
5. Wait until the deposit has seasoned for 2 months. Visit the bank and have them prepare the “bank letter of guarantee” and prepare the documents mentioned on the hand out
6. Visit Immigration and apply for the 1 year Extension of the Stay Permit based upon being over 50/retired