I breastfed both of my babies. It just seemed so much easier than messing with formula, not to mention better for them. They had no problems sleeping, either. My daughter started sleeping through the night at 9 weeks, and my son at 5 weeks. They were definitely getting plenty.

I'm really not sure what reasons would make a mom give up the positive benefits of breastfeeding, to both their babies and to themselves, and use formula. I've never heard any that would have convinced me to do so.