Cribs after 6-9 months??

Kris
We were just given a crib, but I just realized it only for use until 6 months, and not be to used after the baby can roll over/sit up. We live in a small apartment and don't have a lot of space available, thus we were hoping for a crib that could be used for much longer. 
We already have a double bed in the nursery room. This may be a really silly question but..... could a 6 month old go from a crib to a bed? If we put bumpers on the sides obviously? Or is that ridiculous and we should look for and buy a proper long-term crib?