@Helen *****
based on your previous post I see you’re from UK and your husband is French. Therefore you both are entitled to do a border run and get a 30 days visa exemption with another 30 days extension locally.
For applying for an Extension of Stay the French embassy still offers to provide a affidavit letter to confirm income/pension, but unfortunately the UK embassy don’t provide this service anymore. Therefore you’ll need to bank 800K thb in a thai bank if you wish to apply for an extension of stay based on your Non O visa.