Most consider glass catfish to be the best tank mates for bettas. This is due to it being a very docile fish & since bettas are extremely aggressive any fish with even a slightly aggressive nature can have difficulty living with bettas. You did the right thing by adding the betta to the established fish tank with the catfish. Had you done it the other way around, the betta would likely have felt it was "his" tank and as bettas are extremely territorial, he might have seen the other fish as intruding on his "turf" & acted aggressively towards them. Adding the betta to the tank with the catfish meant he was the new kid on the block & aquarium rules were already established. However, this might also have made your Betta feel unsafe in the unfamiliar surroundings which came with already established residents. Even when alone in a tank, bettas need plenty of places to hide when they don't feel safe. These might include broad leafed or other think plants, jars, caves & other types of decorations. Probably the most popular hiding places put into tanks by Betta owners are little clay pots as Bettas seem to love these. So if your Betta is hiding that's normal behavior for this type of fish. As for floating at the top this could indicate he is sick. He might have swim bladder. This should be investigated if your betta seems to be having trouble swimming normally, spends a lot of time floating to the top, sinking to the bottom or listing sideways. It may also seem like it takes him a lot of effort to swim to the bottom from floating or to reach the surface if sinking. Floating/sinking may occur with suddenness such that he may pop up to the top of the water like a cork or sink to the bottom like a stone. Swimmers bladder is most likely due to constipation which can be deadly in bettas. There are several things you can try that could help him (subject for separate question). If this is not it & he just seems to be floating a great deal but does not appear to be having any difficulty swimming this is more likely a reflection of bettas ability to air gulp. Some say this is normal for bettas and they need to surface every few minutes, remaining there a bit longer if they are taking in more air to build a bubble nest. Others say just because bettas can breath surface air doesn't mean they should & it's a reflection of inadequate oxygen in the water. Make sure the water moves constantly, add a bubbler, air stone or live plants & check the water temperature and quality.