S.M.
It's better to ask than to wonder! :) I'd definitely go shopping for the next car seat up. The weight and height requirements are both important. The carrier are great because they're so convenient, I know I was sorry when my first son outgrew his so fast and I had to carry him on my hip everywhere, lol.
What you want now is what they call a convertible car seat - meaning that it can face backwards and forwards. A good example would be the Eddie Bauer 3-n-1 seat or the Britax Roundabout. HTH! :)