If it wasn't a hex, I would have suggested shell-dwelling cichlids Oh well...
Are you set on going for only 1 or 2 individual fish (perhaps a trio of sparkling gouramies, some shrimp, and heavily plant...)?
You could set up a cute little community:
1 male honey gourami (colisa chuna/sota)
3 pygmy cories (make sure they are pygmies - the tank's way too small for normal-sized cories)
5 spotted rasboras
4 male endler's livebearer