Lots of children get a huge amount of security from the enclosed, safe, secure feeling the side of the cot gives. I don't see the point in forcing the issue of moving to a bed until the child is emotionally ready.
All of my children have been at least 3 years old before the sides of the cot came off. At that point, once emotionally ready for the "exposed" feeling of the bed, it is then no stress or hassle to make the change.
So my first suggestion would be the most simple - put the sides back on the cot. If that is not possible, try to recreate the enclosed feeling of the cot sides. You can get bed-dens that enclose the bed, or mosquito net type things.
The climbing is a behaviour issue. Like all unwelcome behaviour, you just teach child that while you can do something, it doesn't mean you should. Most toddlers physically can run across the a road, but you don't let them do it. You teach them that particular behaviour is dangerous as so must stop and not happen again. Same with cot climbing.
I agree to a point however while my child is never without adult supervision near a road, I can't supervise her while she sleeps - for me I'd rather not run the risk - she's a very tall child - bigger than most kids a year older than her so even if she leans on the bars there is a risk she'll topple out.