Mine lives with Kuhlis, otos, and a albino bristlenose. If you have a large enough tank I recommend a few kuhlis. More than 3 if you want to see them though. I would recommend any small tropical bottom feeder, they seem to leave each other alone.
Goldfish are an extremely bad idea, gold fish like cold, highly filtered water. Bettas like warm, still water. Also, neons have a bad habit of being nippy, or the bettas will attack them. I also heard platys work but my betta attacked one so bad that he killed one so it really depends on your fish.