shrimp have a history of being eaten, but are fine as long as they have cover...usually. Corycats (corydoras catfish) are a wonderful addition to a betta community. They are a schooling variety of catfish that have very similar water preferences to bettas. they also don't look anything like bettas, and are both quick and tough, so even a curious or aggressive betta can't do them much harm. They are both easy to feed, as both eat sinking bottom feeder pellets (no worrying about them getting bettas" food and vice versa.) most agree they both have very charming personalities, and they are some of the more commonly kept betta tankmates.
Cories come in many varieties, including pygmy. you should get 4 of these, or about 6 pygmies if you prefer those. If you get cories, only get cories. they are fairly messy
I personally only know of cherry (red) and ghost (clear) varieties of shrimp. I honestly don't know about stocking these, so I'll leave that for someone else..