Personally I don’t like mixing my bettas with other fishes. I’ve lost several bettas because I chose the wrong tank mates. Even though bettas are vicious to one another they can act pretty cowardly when seeing other species of fish. Once I put a goldfish in the tank and it beat up my betta to death.
Other times I put a small snakeskin gourami (Trichogaster pectoralis) I found in the paddy field near my home. When I put it into the tank it was smaller than my betta so I though that my betta would have a small little fish to play and chase around. What I didn’t realize was that a gourami grows much faster than a betta. In two weeks time it was about the same size with my betta and then the role reversed. My betta turned into the one whose being chased around. A snakeskin gourami is a rather vicious fish too. It ripped the fins of my betta and almost killed it.
So what kind of fish/animal you can use as betta tank mates?