could use some advice...

Hi Helen. Welcome to PP first of all. I believe that what your son is doing is just one of those phases that younger children go through. My son never did it, but I have read that plenty do. I can only suggest that you stop him if he is with you, obviously, reinforcing the behaviour by praising him when he stops, and giving lots of cuddles. As for the cot, use cot bumpers to cover the sides and give him a little protection. Have a chat with your health visitor, they have seen everything and may have some ideas or maybe some insight into the causes, and at least offer some support.

Good luck and let us know how you get on.