It's definitely possible to sling for a long time. I did it until ds was about 18 mos. He was just too heavy for me at that point, but he still liked it. I would recommend not getting a padded sling. They're a bit bulky and definitey hotter. My cousin had a Maya wrap, and she made me one very similar. I packed away my OTSBH and started using the one she made me. It was cooler and more comfortable with a bigger baby.
One sling a recommend against is the Native Baby Carrier (I think that's what it's called). It can't be adjusted (except permanantly with a sewing machine). A friend lent me one when ds was born, and it was uncomfortable, too loose, and hung down too low. It just didn't feel very secure, and ds didn't like it either. As soon as I switched to the OTSBH he was much more content in the sling. I like the ones with rings because you can have them a bit loose for putting baby in, and then tighten them up to make everyone comfortable and safe.
My ds's favorite position at your baby's age was the "kangaroo" position, where he faced forward with his legs criss-crossed and folded againsted his belly inside the sling. I know it sounds uncomfortable, but they're really flexible at that age. It's very easy to get him into the sling in that position, too. You just fold up his legs, drop him into the sling, and tighten it up. He loved being tight against me but being able to see everything. I really liked the postition, too. He felt very secure against me, and he wasn't constantly trying to turn to see something. People around here don't use slings, either, and some made some funny comments (especially with that position -- "where are his legs?" or "does he have any legs?!?"), but so what, we were happy.
I looked at the link in kofduke's post, and it looks really good! They have so much info! I wish I'd had it when I was looking for slings.