@Cindy ******
you are trying to do what Thais will tell you not to do "don't think too much".
You are wanting a type O visa extension based on retirement as your final objective. The very first thing you must do is get a Thai bank account in your name only. Then you must transfer into your new Thai bank account at least bt800,000 direct deposit showing that it came from an overseas source.
Once you have the money in your bank account you can apply with immigration for the first step in getting your eventual one year extension, and that is getting your 90 day type O visa extension at a cost of bt2000 from immigration. Don't touch the money in your bank account. After it has been in there for at least two full months, and when you have less than 30 days left on the 90 day extension, you apply for your 1 year extension, and at the same time present any other documents they might ask for at a cost of bt1900. After you get your one year extension, the bt800,000+ has to stay in your account for three more months, then for the rest of the year it can never drop below bt400,000 . At least 2 months before your next one year extension the balance has to be back at bt800,000+.
It is very easy to do, and understand. The hardest part of the whole thing will be trying to get a Thai bank account on a tourist visa, but by checking every bank you find, even if it is the same bank just a different branch, still check. After getting that, the rest is very easy, and, immigration is actually lots of help when you have questions. They have a list they give you of what is needed, but your Thai bank account is the most important. Good luck