Bettas don't live in small pools of water in the wild, they live in huge areas of shallow slow moving water - places like rice paddies. They can survive a dry season in small pools of water but surviving is not thriving. They cope till it rains again.
I have red cherry shrimp. They used to be in a 54 litre tank (14 gallons) till we altered the kitchen, there was no longer anywhere for it to go, so I had to close that tank. The shrimps and the few fish in with them were moved into my 180 litre tank.
In the 180 litre tank the shrimps swim all over, especially the males when the females released their "come and find me" pheromones. Personally I would never confine my cherry shrimps to a small tank.
Try shrimps if you want, it's just not something I would do.