@Wayne *********
Cool about the OX visa, don't know much about them.
I would re-approach the Thai consulate and ask specifically if you get the Non-OX visa from them whether they will sell a Non-O (dependent) visa to your wife. That would be the easiest way forward. Explain what you are trying to do and ask them the best way to accomplish that (you on a non-OX and your wife piggy-backing off that visa as your spouse).
Second best is getting a Tourist Visa (60 days) for your wife or even settle for visa-exempt entry (45 days) and you don't have to even get a visa.
Stay away from the STV visa. It is definitely and absolutely not convertible to anything else in Thailand. It was never a good deal and is on its way to a timely natural death anyway.
To go into the reason that I say better for your wife to come to Thailand with a Non-O visa herself is that it's not really clear to me whether she can get a Non-O visa in Thailand for the specific purpose of getting an extension of stay for reason of being a dependent. You can get a Non-O visa in Thailand, BUT there seems to be some troubling wording about that the Non-O visa needs to come from outside Thailand for purpose of a dependent visa.
Finally, I would also contact the Phuket Immigration Volunteers (great group, very knowledgable and helpful) by email about how exactly to do what you are trying to do -- get your wife in a position to piggyback off your visa and they may have good advice.
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