Cookie,
Part of me thinks that his beahviour in the bed means he is not ready?
This part of you message makes me think that deep down you feel he isnt ready.

With my DS he was walking at 10 months and at 13 months was climbing out of the cot all the time he would climb up onto the rail and just drop down onto the floor. It was very dangerous. My cot didnt turn into a toddler bed but one side dropped down and i just un-did the screws and took of the side. This way it was still his cot but without 1 side. I tried him in it for few times to see how he went. I didnt have a mattress to put on the floor so i used the lounge cushions at 1st. we had issues with him climbing off the bed and being naughty so i put the cot back together again and tried again a month later. he must have learnt if he wanted no side that he had to stay there.

So my point is if you could take the side off to try him then you'll see how he goes. saves buying the bed only to find out he's not ready. After 6 months with the side off we went to a BIG single bed for him and he's slept well ever since.

GL