M.B.
Carolyn,
When in doubt, cut out the milk. You are breastfeeding, and that is plenty for him right now, in fact, right up until a year of age. If you can try pumping, and give him that in a bottle, that might help, too. You've got the clues: extra crampy after formula. Trust your instincts.
Milk is milk. I don't know that it can be treated so that little tummies can tolerate it better - go with your gut reaction, it sounds like you know your baby.
He doesn't NEED formula. He receives all he needs in one nice, neat little package deal from you.
Good luck, and congratulations on your little boy being breastfed so long and so well!
M.