Upon expiration of my ED-Visa (end of November), I would like to convert to a O-Marriage Visa. Is this doable at immigration in Thailand, or will we have to go to immigration in an other country to do this?

Thanks & cheers.

It is doable, but will in most cases require that you apply (together with your wife) in Bangkok. Prepare all documents you require and season the money if you go for that route. You can apply 30 days before your current permisison ends and are advise to do so. That way you have time if you need more docuemtns or are denied the conversion.

If you are on ED extension, you will also need a letter from the school stating that you have concluded (or dropped out from) your studies. This is needed in order to close your ED extension file.