as with everything in Thailand... It depends on the official. It is the list for foreign woman married to Thai men specifically (so not really useful for foreign men married to Thai women), but if there is an interest, I'll ask
have you asked in the Expat woman with Thai partners group about whether your baby can get Thai citizenship without getting married? My guess is, you would need more proof or documentats from the fathers side. Personally I would probably get married before the baby is born because it will probably make your family life much easier.