Bettas and goldfish need very different temp ranges to be happy.
To keep one happy, the other must suffer. Even the middle ground... neither will be happy.
Dont get rid of one fish just to get another. Thats just bad pet ownership.
To be perfectly honest, and I dont mean to offend...
If you're considering Breeding but are willing to get rid of another fish as well as put two highly incompatible fish types together, I dont think you're prepared to breed fish and the challenges that will present themselves from it.