if you want to put him in a bed for naps or night time he'll be fine - but only if he can get off the bed on his own safely already!
don't worry about him falling out of bed once you left him, just put another mattress on the floor, if he falls out he'll be fine, I mean it's a very small distance and onto a soft surface!
just make sure there's no gap between the bottom of the bed and the mattress on the floor, if he wakes up with his head or limbs stuck he'll cry his face off!
I wouldn't bother with a cot rail either, such a nuisance for you to try to shuffle off the bed once he's asleep!
if him getting cold is a problem, get him some grobags.
use waterproof sheets in case his nappy leaks - if that happens a lot give him a bigger size nappy for the night
make sure the floor is clear from toys, clothes etc to avoid any tripping over and injuries in the night for him or you.
you probably have safety plugs in electric sockets already - if not, do it now.
most importantly, which ever bedroom he will sleep in put a stair gate on the door, so if he wakes up he won't be able to get out of that room!
I personally prefer a cot for them as long as possible, but as you are comfort feeding him to fall asleep it is difficult, I get that.
our DS5 is 3 in May and although he sleeps in various beds at times (ours, brothers, spare bed in his room, on the floor on a mattress next to our bed for naps or all night) he will graduate to big bed properly after his birthday for various practical reasons.
I hope this is helpful