The Ergo also fits that criteria.

And any mei-tai-style carrier. I still carry DS in the mei-tai and he's over 2 years. Remember though that anything that carries on the front will put strain on the back - back carriers will protect your spine a fair bit if you take care on your posture (as in every-day posture).

There's a group called ozbabycarriers (PM me if you'd like the link) that have a lot of information and even a lending service so you can try before you buy.

good luck!