I would move up from something like pinky mice. Pinkies are usually for much smaller snakes like colubrid hatchlings. I would try to select a mouse that is just a bit wider than your snakes width. There are many opinions on boa feeding, but I usually tell people to feed one appropriately sized animal once a week for at least the first couple years of life. Once you have a ~3 year old snake you can start offering much larger and spaced out meals.