You should definitely throw a heater in there. Even if your atmospheric temperature is appropriate, it's probably not stable. Unstable temperatures lower your betta's immune system and cause quite a bit of stress. I think there's a Tetra heater at Walmart that is made for small tanks that a lot of members here use without problems which keeps your temperature at ~78ºF. And stable.
As for the tank mates, I think two gallons is too small for anything else to be added. Maybe a shrimp? I think most people suggest a minimum of five gallons for ADFs because they like to be in pairs, but I could be wrong. The last thing I can think of is a snanil, if that's something that interests you.