How can I obtain a Non-O visa in Thailand after my initial 60-day stay?

No need to leave Thailand to apply the non o visa

I just did the marriage visa. It's a real pain in the neck. Probably worth it if you intend to stay for year or more. I hired someone to do it for me. It was probably expensive but having someone to navigate the paperwork who also has connections makes life easier.

You will need a bank account in your own name. Only a few banks can accept overseas transfers over 50,000THB. Plan to park 400,000K in the bank for a couple of months.

You will need a bunch of other paperwork, wife's address, tambon card (whatever it's called), original marriage certificate, photos of you and your wife, etc etc.

If you have at least 15 days left before exemption expires, you can file a TM87 to change your Visa status to Non O. Financial proof required tho (400k baht in a Thai bank)

Are you planning on staying in Thailand indefinitely?

If so, you can apply for the 90 day Non-O based on marriage. It will require you to have 400,000 baht in a bank account in your name only, and your wife will need to accompany you to immigration.

If you are just trying to extend your time during the visit, after you get your 30+30 on visa exempt, you can then apply for the 60 day visiting Thai family extension.

You can apply in Thailand