I don't understand why your friends push you so hard, is it their business? if i am you, i will politely
talk to them " please respect to me and my decision, i know it is the best for my baby, thanks ."
in your case, i think you have explained to them so many times, it seems that it is meanlingless to tell them how good is BF, no need to care about them,
they only share 0.0000 1% in your life, you should care about your baby's health, development. One day, you can prove to everyone that bf is the best for your baby, because your baby is more healthier than the formular baby, more clever. Trust yourself.