Far & away the best breastfeeding friendly carrier I've found is the Maya Wrap. It's a 'ring sling' (as opposed to a 'pocket sling'), so it's very adjustable--but without the sometimes cumbersome padding of some other ring slings. The maya wrap also has a long, broad tail -- perfect for throwing over my LO (for modesty or to decrease distractions). Both my sons have/do nurse in the maya wrap all the time. DS2 likes to ride in the sling on my hip or in front in an upright carry. When it's time to nurse, I loosen the sling slightly, tip him to the side & we're good to go. I've nursed him in the sling while standing watching my DS1 play on the playground, while boarding an airplane, while walking to an appointment, etc. Now that he's getting older & likes to squirm while he nurses, I find myself using the sling as a 'containment' device. Some hints for getting started:
* Wait until your newborn has figured out a good latch & your breastfeeding feels solid.
* Wear a nursing shirt (or no shirt)...pulling your shirt up from under the sling can slow you down & get in the way.
* Practice at home, when your LO isn't hungry, just to get the positioning.
* If you wear your sling over the right shoulder, nursing on the left side is much easier (away from the rings)... try that side first. Tip her to the left side with the sling loose, supporting her with your left arm outside the sling. When your position is good, use your right hand to tighten the sling to support her. While she's working on her head support, you will probably need to keep your left arm under her & perhaps hold your breast with your right hand. Even so, you may find that the sling offers enough support to stand in for a boppy.
* When you're ready to try the right side, I've found the best method is to loosen the sling ALOT, keeping the inside rail of the sling very loose, while tightening the outside rail a bit. I also tend to slide the rings high up onto my shoulder to make room for DS2's head. Otherwise, follow the same instructions above.
Whew! I hope this was helpful! I've found that being able to nurse in the sling makes it much more comfortable for me to nurse anytime & anywhere. Good luck!