HotI I stopped using the infant insert in the ergo sport around 3 months of age - mind you, DS has excellent head control and is not a small baby by any stretch of the imagination Try him out in it (when you find it!) and see how you go, I've also heard that a rolled up terry flat or small towel in the bottom is a suitable option if they need boosting up a little.

As for favourite carrier - I'd have to go the beco butterfly2. Way more adjustable than the ergo, more comfortable and has a built in newborn insert whereas they have to be bought separately with the ergos. Plus the becos have nicer patterns