Anna, when you say "bowl/vase", it isn't one of those vases with a plant in it is it? If so, get him in something else fast. That set-up will kill him.

I have one betta in a 5 gallon aquarium with a pleco, and three neon tetras. He seems very happy in there. I have my other two bettas in a one gallon tank each. They both have adequate filtration and lights in the covers. They seem extremely happy, but I think anything smaller would get dirty too fast and not have enough room for a plant or a cave/cup for hiding.

Can we see pics? Pretty please with sugar on top?