I can't help with the cot buuut I put my boys into 'big boy beds' ....I just got one of those side rails that has two 'arms' that slide under the mattress. DS#1 needed his for a few weeks as he rolls all around his bed and DS#2 only needed his for a few days as he practically does not move in bed at all.

A friend of mine just put some cushions from the lounge on her sons floor.....

Sorry I cannot be of much more help.
xxxx