A lot of them are good nowadays, good second hand market on ebay as well. We have the deuter kid comfort II – you will not go wrong with this. Also liked the look of the bush babys.
If you’re using it for any proper hiking, you really need a sturdy backpack like the ones in the photos above. They have sophisticated straps that allow you to distribute the weight very effectively. Trying to carry a wee man in a lightweight baby bjorn type carrier is OK for a bit, but would get seriously uncomfortable on longer walks.
Our lad is a healthy 11 kilos (He’s not even one yet :)), and it’s a good workout taking him out for a hike. We went for a circuit of Haweswater (about 10 miles) and it nearly finished me off. I’ve not hiked with a heavy pack for years, though, so am hoping you get used to it.