It is really good to finally read stuff about this. I've been surprised from hearing that so many womn actually choose not to breastfeed not to damage their breasts, ugh.

These articles mention that there is no actual evidence to say that breast feeding will cause your breasts to sag.

Their study shows that there are other factors that affect breast sagging:

The study, published in Aesthetic Surgery Journal, showed that greater age, higher BMI, greater number of pregnancies, larger pre-pregnancy bra cup size and history of smoking were significant risk factors in the development of sagging breasts.