Once you get a bank account and put in the 800,000, getting a non-o for the It is not difficult without an agent. After 3 months you roll into a 12 month extension of stay for "purpose of retirement". No such thing as " retirement visa". The cost doing it yourself is 2000 baht. I just changed country passports and am in the process now. Lived here for many years
I am 75, been here 13+ years. Best to get 60 day tourist visa at your embassy/consulate, then you can get additional 30 days here at immigration for 1900 baht. That gives you plenty of time to get bank account and seed 800,000 baht. It is still best to use agent for 1st time as immigration is not easy at first.
I always have done my own visa "stuff", however, it constantly changes. If you are coming to Phuket, I can send you in the right direction.
All you need, is to fill out a TM7, photo, copy home page and your current visa/stamp, and 1900 baht. Office opens at 8.30 Phuket Town, so if you arrive 30 minutes early, you'll be ahead of the masses. The office is downstairs, front left of building.
I am 75, on my 14th year. Always handled my visas. I am on extension of stay based on retirement. That is what the so called retirement visa is(365 day ext.of stay for purpose of retirement). You could enter on 30 day stamp in and get a 30 day ext. Message me if you want more info.
Even a U. S. Citizen returning to U. S. from Mexico needs a valid U. S. Passport. Been in effect for at least 15 years. Last time, about 15 years ago that I crossed Mexico to U. S, scanned my passport, and the agent said, "nobody loves you", which meant, nothing negative on the computer