What is the best process for getting a 30-day visa extension in Thailand?

To make the most out of your time, you fly into Bangkok, so spend two days there. The very first day in Bangkok after you arrive, and checked into a hotel the day/night before, immediately go to the immigration office at IT Square at Laksi. At that office you can get your 30 day extension right away, and the time is added on to your original entry stamp. This is much better than having to wait until your last week at Pattaya to extend it. It only takes an extra day in Bangkok, and it is done. In Bangkok you can apply for your extension when you have less than 45 days on your entry. You are entering on a 30 day visa exempt stamp so you can apply for your 30 day extension immediately in Bangkok.vask your hotel in Bangkok for a copy of your TM30 they filed, and your set in case it isn't in the system yet. Stay at a regular hotel, not an Airbnb, as many of them don't file a TM30, that is required.

Why don't you get your initial Non-O Visa before you travel so on arrival you'll get 90 and a better chance of opening a Thai bank account (if you don't have one) which is needed for the seasoned funds for your extension.

Apply for a day tourist visa before you come to Thailand

There's no such thing as a 15-month retirement visa. You get a 90-day non-O (over 50) visa, which you can then extend for a further 12 months

At the Jomtien immigration office you can only apply for a tourist extension during your final week of stay. So you would have to wait approximately 23 days before you could apply for your 30 day extension.