Yeah, females can be kept together. But you wouldn't want just a couple...the more, the better. Because even though females can live together they can still be aggressive and in a large group the aggression is spread around. If you had, say, only three girls then two might gang up on the other.
So I would get five or six females. You don't want to mix genders... they will end up fighting. Breeding bettas is actually quite tricky and the breeding pair is only kept together while breeding since otherwise they might each other. Even when doing everything right you can still end up with fatalities
. Oh, and getting them to breed is often the easy part
. Raising the fry is a whole other story...
If you don't want a group of females then I would get a single male and some other peaceful community fish. Bottom-dwellers such as cory cats and oto cats are good since the bettas barely notice them. African Dwarf Frogs are usually good tankmates with bettas...but watch them carefully at first. The frogs seem to prefer having at least one buddy so I'd get a pair. The only annoying thing with the frogs is that they aren't always the best at finding food so you have to target-feed or hand-feed them. They also do best on frozen or live foods rather then flakes and pellets. But bettas are the same way so I think it should work out
Snails are neat but require special care so research first. Apple Snails are great if you are new to snails...they are hardy, peaceful, and come in a bunch of varieties. They do need to be fed different foods such as vegetables. They don't eat fish poop like some people think
Also, make sure the filter isn't too strong if you have a male. Sometimes they have trouble swimming and making bubblenests. Luckily there are many adjustable filters and there are other ways to slow the current such as getting lots of plants.