Goldfish are not feeders, as they have 0 nutritional value to your Bass. They also have a very high likelihood of carrying parasites that can and will harm your Bass.
If you want to breed small fish for the large one to play with, like I do, then I suggest Mollys, Swordtails, or Guppies. These 3 are livebearers, and breed extremely easy. I think Guppies are the easiest to breed, but they are also the smallest of the 3, with Mollys being the largest. The hardest to breed of these 3 are the Swordtails, as the males will overly annoy the females if not watched carefully and the numbers limited strickly.