Hi Cricket,

I was using the Moby on me son until about 2 weeks ago,It was just getting a little annoying to put it on.I also found as he got heavier he would slide down my front after a while.
I'm not using a sling anymore, I'm using the Ergo Baby.It's really worth having a look at.It can be used until they are toddlers and it feels like you are carrying nothing.Sam weighs about 8.5kg(very big for his age).
I would definitely pop in to your local baby shop and try it, I couldn't live without it!.
Hope that helps.