Yeah if he cannot handle cories... I wouldn't know what to recommend. I have had mine with danios (they learned he's the man :p) balloon mollies (more docile than regular mollies), guppies (male and female), tetra, snails...
But it definitely depends on your betta's attitude. One of my males would tear everything to shreds. Another would hide. The other couldn't care less... and another would be inclined to chase.
What I learned, is that you should take out the betta, rearrange the plants and ornaments, put the other fish in, float the betta in a clear container or bag (or breeder's net if you have one), then introduce him. Then it is firstly not his territory right off the bat, and the rearranging will have everyone choose new territory anyways.
Breed for the breed, not for the money; the words any REAL breeder would understand.
You must know nothing in order to know all, for all is nothing and nothing is for all.