Preferably I would say no any other fish in the tank, usually a 10 gallon is the minimum when it comes to a Betta fish with any other fish.
You could add a snail or two, maybe a few shrimps, or even African Dwarf Frogs. Should consider getting live plants if you're into shrimps, since shrimps sometimes can become a snack for your Betta. Live plants give them more survivability as they can run off and hide. I'm not sure about ADFs though, apparently they're quite territorial like Bettas. . And they're social too, so you'll need two or more.
So yeah, either snails, shrimps or ADFs (maybe), but fishies, not really. .