I have two community tanks with male Betta in them and one with a group of females. I find that the type of plant really doesn't bother them, just as long as there are plenty of spots to hide away.
One of my Betta absolutely loves a plant called riccia fluitans when it is used as a floating plant. It provides him shade and he enjoys making bubble nests in it. My Betta sorority seem to enjoy it as well.
As for the type of fish to go for, I'd always recommend something like an ember tetra. They are quite small, fast enough to get away from a Betta if it decides to chase one and they are not nippy. They like to spend their time in the upper and mid of the tank, so they do share the space with my Betta but there has never been an issue.
An obvious choice would also be Corydora for the floor level and Otocinclus to help them with clean up.