M.F.
Ergo Baby Carrier - hands down.
I still frequently carry my 4-year-old in it, and I can still carry my soon-to-be 7-year-old in it (not for very long, but it works in a pinch).
I ordered mine many years ago from www.myfavoritebabycarrier.com. They offer a 90-day $$-back guarantee, so if on the very low chance you aren't happy with it....
Best wishes-
M.