What is the process for UK citizens to obtain a Non-Immigration O Visa and extend it in Thailand as a trailing spouse?

We got our marriage certificate legalised through HMGov website then took it to the Thai embassy in London

if you BOTH apply for Non-O visas (based on retirement) in the UK (they won't issue 90 day Non-O based on trailing spouse) and then come in, you get the money banked, do the year extension and then have your husband apply for the trailing spouse extension it MIGHT work OR it might not..

You make sure you get that brit marriage certificate legalized BEFORE you wing your way here as you can't do it once you're here. It's done thru Milton Keynes, post on a brits in thailand and ask about the process, That WILL throw you off the rails if you don't have it done before you come here because you'd have to mail it back to get it done.