The OP asked for a 30 day extension and was told the right answer, cannot have one. Going back and asking for a 60 day Visit Thai Family extension while accompanied by his wife and with the correct documentation (assuming the marriage is registered in Thailand) will get a different response.
This has never been possible since a conversion from a tourist entry stamp to a Non-O based on retirement requires a Thai bank account with 800k (this is not just a requirement for the extension)
Agreed, enter on a Non-O, open a bank account and transfer 800k, get a re-entry permit for your Vietnam trip and, on your return to Thailand and after your 800k has seasoned for 2 months, apply for your 12 month extension then get a re-entry permit when your 12 months is inked in for your return later next year.