my sister gave me my nephews cot when he was 15 months and put him in a big bid with a safety rail. she only did it because i was a couple of months away from having DS and she had offered me the cot. he went alright with it, but still woke in the night some nights, and had trouble going to sleep in there at the start of the night, and they used to have too sit next to him in the dark until he fell asleep. some nights it would take an hour and they would end up falling asleep on the floor next to him.
if your DS is bumping into the side of the cot and waking up, he will prob just do the same in a bed and bump into the wall, or the safety rail if you were planning on putting one up, otherwise rolling out of bed. but all kids are different i suppose, so the only way you will know is by trying it.
for us it would never have worked, we tried when DS was 20 months and it was a nightmare, we didn't even get through the first hour before we put him back in the cot. he's now 22 months and still in it, and we have bought a new cot for the new bub due in august so if DS is still in the cot then it doesn't matter too much.