Honestly, human breast milk would be fantastic. You could know that it was at least as consensual as any other form of labor, the women selling it would be compensated decently (after all, they’d need to take hormones and eat a balanced diet in order to produce milk constantly, so ya gotta make sure you’re keeping them healthy), it would be more nutritionally balanced for human consumption, and so on. Plus, less methane emissions, since human farts aren’t nearly as noxious as cow farts.

I can’t see any real downside to it, aside from the fact that a gallon of milk would cost something like $100.