Anonymous participant 254 that's bad information. Thai consulates treat the evisa system as if you were physically handing in your passport which means they expect you to remain in the country you apply in. In fact the post you've commented on is a classic example of just that
You need to maintain it at a minimum of 800k for 3 months after you get your extension and never drop below 400k until your next extension is granted at which point you can withdraw it.
Very easy to do it yourself and no getting stuck using agents for the foreseeable. If you are already inside Thailand you need to have between 15 and 21 days left on your current stamp to apply for the Non-O visa based on retirement, visit your local immigration office for their exact requirements as they all vary slightly. If your not yet in Thailand then applying for the Non-O before you travel is the best idea, especially as there will be no need for a return flight
You know what the solution is, you even mentioned it yourself. You are not a genuine tourist so get the visa that applies to your situation, 400k baht is not a huge amount of money and you don't even need to maintain it in the bank for longer than a couple of months. I'm sure you'll easily spend that in a year in Thailand