The Troll Sun cot can be converted to a junior bed and you will need this conversion kit. It has a lower bed end and two side pieces. The bed head (one of the cot ends), the base and the mattress will be reused from the cot.
Once converted your child will be able to get in and out of the bed unassisted and you can put off the purchase of a single bed for a few years yet. The smaller junior bed also allows for more fun on the floor than a single bed plus it is much closer to the ground should your child take a little while adjusting to sleeping without the rail sides.