Quoting Amber :]:" I was told that when the baby's bigger you can use them to carry on your hip."
It'll still sag
I'm not trying to be rude at all, I'm just pretty knowledgeable about babywearing and no experienced babywearer or babywearing educator would recommend using a stretchy wrap past about 15 pounds (unless they're one of the two I mentioned that are stretch hybrids) for a comfortable, supportive carry. Lots of people love them for the tiny squish stage, but they're pretty useless after that. A better choice would be a woven wrap which would offer more support, are generally thinner and less hot, and are safe for all carries. I have a few (I think right now I'm at 6 but I'm too lazy to add it up) and I comfortably carry my 30 pound almost 2 year old in them. Another option that would be great for small babies and hip carries when they're older would be a ring sling or a wrap conversion ring sling.