Hi, I have not had children, so I will not pretend to know how your breast feel or have changed, but I was not sure if you have tried this one, I tried a few and this one is the one I like best, the thing I like is that you can put the guards in and out of the bra as you need to, plus it works on its own as a great gym/workout bra as well. Other than that I would suggest may be asking your instructor, they may have an idea of where best to look.
Ladies Cool Chest Guard
http://www.playwell.co.uk/store/acat...rotection.html