What are the best options for obtaining a longer-term visa in Thailand for someone needing to return to the UK every few months?

When you already HAVE a Thai bank account, you can transfer the 800k฿ already 2 months before you come to Thailand. Then when you already have the non imm O as

@James *******

mentions, you can ask for the year extension after about 60 days already. With a multiple re-entry permit. However for this visa nowadays, one asks quite some (Insurance) requirements.

Obtain the Non O as retiree in your home country. That will give you 90 days on entry.

Then open Thai bank account in your name only and transfer internationally 800,000 Thai baht into it.

Then apply for the one year extension of stay as retiree...get a multiple entry reentry permit too.

Then you can come and go as you need for an entire year.

Renew it at end of each year.

This will allow you freedom to travel as you wish.

I don't think you will have the time to enter the country on a 30 day visa exempt or a 60 day tourist visa, then get the 800K baht in a thai bank account in your name only apply for the 90 day Non-O visa and then the year extension before you would leave the country again. You say you need to go back every 2 or 3 months and it takes right around 3 months to pull of going from a visa exempt/tourist visa entry to a Non-O and then a year extension.

Just get a single entry tourist visa, come in, get stamped in for 60 days and extend that by 30 at the immigrations, that will give you the 3 months you want to be here and would be the least problematic