We just changed ds who is 2 and a half, and have had no problems. However when he was just under 2 we tried, by converting his cot to a bed, and it didn't take. He was wandering out all night, and after a couple of days would end up in his portacot so he would sleep. We decided to wait a bit longer.
This time we tried it has been a breeze. We had decided to have the cot stay in the and have them both set up at the same time. We have a bed rail, so to get out of bed he has to climb down the bottom. He doesn't even climb out! He did for the second day or so but seems to have forgotten he can get out, and hasn't battered an eyelid at his cot. He takes his teddies to bed, and now a couple of toys as well and we put a red doona cover on with lots of cars which he loves.
Good luck