There are no guaranteed "good" tankmates for bettas. Some bettas will tolerate other fish in the aquarium, and some get downright vicious with other fish. And that includes snails, too. I honestly think most bettas prefer solitude rather than companionship, but that's just my personal experience with them.
Be VERY careful. Bettas may appear sweet natured by day with other fish but their nasty side may come out at night when you're not around, and you may wake up to an injured fish in the tank. Not to scare you, but just be aware that this can happen. I would have a Plan B (ie. another tank) as a backup if it doesn't work out.