What are the requirements to change from a COVID extension to a NON-O Dependent Spouse visa in Thailand?

you get documentation from the employer (a letter stating they know you're going to 'piggy back' on their employees visa/extension) his contract, work permit, documents from the company, marriage certificate (possibly certified). You need a minimum of 15 days on your current stamp to apply in section C-1 for the 90 day Non-O visa based on being married to someone on a long term extension who legally works here, you pay the 2000baht, get a 14 day under consideration stamp, go back on that date, get a Non-O visa and a new 90 day stamp inked in. THEN you wait until you have 45 days or less left on the stamp go back to the immigration office with new documentation and apply for a year extension for the same reason (married to a foreigner who legally works here).

Either you or your husbands HR dept should go to immigrations get the hand out from section C-1 that lists what documents you need to apply for the 90 day Non-O visa AND get the hand out that you need to apply for the year extension AFTER you get that visa issued too, so you know what you're doing.