I breastfed successfully while xfitting with only one incidence of mastitis, but that was because my child had a hulk appetite and I was not always great about cleaning up after he finished or after pumping.
Ditto on making sure you're drinking enough water. I personally found that by eating primal/paleo, my breast milk was very rich with good fat for the baby and he had very little gas/stomach problems. The only way to go in my opinion!
Aesthetically though... even with eating clean w/ a cheat 2x a week and xfitting 4 times a week, I didn't see good results until after breast feeding, which for me was one year. I just didn't get that really cut look again until then, BUT whatever! it's our babies!
Good luck to you!