I'll be the voice of dissent. I have never seen anyone wear a NN that fit them properly. The company makes them too big, and even the pictures of their models show them wearing them too big. Your baby should be worn up close snug against your body, several inches above your belly-button.
The hotsling carriers fit so much better, and the size charts are very accurate if you measure yourself. It will make all the difference in the world to your back as your baby gets heavier if your sling fits you properly.
Mama to "The Fantastic Four":
DS 02
DD 06
DS 09
DD 12