Deniece Paterson all you can do is try. Is it even possible to get an extension in Thailand on the back of someone's O-A visa? I always thought the person you want to ride on, needed to be on an extension themselves, and not a visa entry. I could be wrong.
Certificate of criminal record clearance from the UK (ACRO, or issued by the police) or Ireland
Financial evidence showing monthly income of not less than 65,000 THB (approx. £1,625) or having the current balance of 800,000 THB (approx. £20,000), e.g. bank statements, proof of earnings, for at least 1 month
If you wish to be accompanied by spouse, the marriage certificate will be attached. But your spouse will be granted Non-Immigrant “O” instead of “O-A”(Long Stay)