I, personally, would breast-feed if I could, if I had my own baby. However, when and if I ever want a child/children, I may adopt...
I will say, however, that breast-feeding is okay for vegans, in my opinion. A mother willingly feeding her child/children on her own breast milk is different from a human abusing a calf and cow and taking the cow's milk to be sold for human consumption. Whereas the cattle and calves are abused and separated for the milk to be taken without the mother cow's consent, a human mother with a newborn baby/babies who wishes to breast-feed, and is able to do so, will usually willingly give her nourishing and healthy milk to her child/children, and there is no direct abuse of cattle involved...
Best of luck.