There are no fixed guidelines on when your child should go into a bed instead of a cot, so it is up to the parent. My daughter is nearly one and is still in a cot, but we are putting her into a bed as she keeps leaning right over the bars, which was a problem as she has nearly fallen over them several times.
There are various things that you can buy to aid the transition from cot to bed such as bed sides (they look a bit like the ones on hospital beds) but you do not need these we are putting a spare duvet on the floor by the side of the bed, but anything soft will do. Also make sure that you have a gate either across the child’s door or at the top of the stairs to make sure your child doesn’t fall down the stairs in the night.