We got our eldest a duvet when he turned one and took the sides off of his cot bed when he was two. Once he realised he could get up any time he started waking in the night and coming in to our room. We put him straight back to bed, after a couple of weeks we got one of these to help him understand when it’s time to get up, it’s helped a lot.
Son number two got a duvet for his first birthday also. When he’s two and his brother is three we’ll probably get the eldest a junior bed and move the youngest into the cot bed with the side off.
Cot beds are low enough that you probably won’t need a side rail thing – ours fell out of bed a few times but that soon stops and it’s low enough (8-10″) that he didn’t hurt himself, just woke up with a jump.