That really depends on the attitude/personality of your betta. I would first put him in by himself and watch to see how much he flares at his own reflection in the glass. If he seems extremely aggressive towards it I might consider leaving him on his own. However if he doesn't seem to be affected by it you could put him with a few different fish. Neons may be a bit sensitive to put in with him by themselves in a small space. We once had a 2 Gal with a gorgeous pink Betta and his companion was a frog (African Dwarf) . They lived happily and finally we moved the frog out so he would have more room to explore in the 55Gal. So like I was saying, it all depends on the Betta. As I have said already, Blackskirt Tetras get along well with Bettas (in my personal experiences), Goldskirts also do the same, and I would recommend getting 3 of them so they can school. I'm sure lots of other tetras would work also, but this is with my personal experience!