some things to house w/ a betta if you really want to:
1) shrimp. some bettas may decide that shrimp are a good snack though, so i recommend ghost/glass shrimp as they are very inexpensive but just as cute and interesting as any other shrimp species.
2) snails. Again, some bettas will see snails as a snack, so select the larger ones that will be hard to eat. certain snails have more specific needs, so research the species and requirements of any you plan to purchase. zebra snails are a very good choice and they are very pretty. snails also may require supplements if there is not enough calcium in the tank for them. soft shell is a pretty common problem with snails, so keep that in mind.
3) corydoras catfish. corys are a wonderful and peaceful bottom-dwelling fish that add a lot of life to the tank. they do require a minimum of 10-20 gallons however, depending on the species (again, research!). They are a shoaling fish so you will need to buy multiple fish for them to really be happy. 5-7 is a good number for a smaller tank. some species are more difficult to keep, so select the best one for your skill level.
4) Harlequin Rasboras. One of the most peaceful of schooling fish and small enough to house in a ten gallon comfortably. Most people assume that it is the betta that will be aggressive towards other fish but usually it is the opposite. most tetras/barbs are notorious fin-nippers and the flowing fins of a betta fish are irresistible to them. rasboras are very peaceful, lovely fish and get along with bettas quite well. again, a minimum of 5-7 fish is required for them to be happiest. in the event that your betta is aggressive to them, they are fast swimmers and will probably be able to avoid him. having a heavily planted/decorated tank is a good idea for these fish.
when purchasing any fish/invert research thoroughly before buying! every animal has it’s own specific needs, so make sure you know as much as you can about each before purchasing. It is also good to know the temperament of your betta. some bettas couldn’t care less about tank makes but others are very aggressive. it’s hard to know until adding tank mates, so be warned. these are only suggestions.