Best choice you could make. Betta does so much better alone, except for a few wild species.I decided to let him stay solitary.
Adding small shrimps like Neocaridina is risky especially for eggs, naupliis, zoeas, mysis. At older stage, it will depends on Betta's character. I noticed mine didn't pay attention to adults Neocaridina or Amano but used fertility regulation