Sorry for any typos, I'm on my iPad. Haha
First off, there are a few things you need to ask to help decide which fish would suit your tank.
1. What size are their tanks?
The minimum size tank for tank-mates with betas is a 5 gallon tank, which can only handle snails and shrimp. Tanks upwards of ten gallons are needed for other fish.
2. What are your water conditions?
Different fish prefer different water hardness, ph, and temperature levels.
3. Are you using aquarium salt regularly?
Using aquarium salt regularly is actually bad for your fish's health. It is a medicine that is usually used in treating external infections such as fin rot and ich. When used regularly, the fish will become used to having it in its environment, so if you need to cure fin rot, aquarium salt will do nothing. It's like taking Tylenol every day whether you need it or not.
Hope I helped! (: