My son started to climb out of his crib somewhere between a year and 15 months. (He did everything early.) Remember, as the baby grows you lower the bottom of the crib to keep the baby from falling out. It is raised when they are first born, for easy access and they don't roll. Since the crib was lower to the ground and very movable, he had plenty of bars to grab on to, so he could climb out. At 18 months he was in his "big boy bed", because his sister was born. His bed is a full size "captains Bed" that has stairs that slide in and out of the side of the bed. I bought 2 side rails that you can slide between the mattresses, (in my case it was the mattress and the base of the bed). The funny thing is, with this bed he did not climb out, because I would slide the stairs in when he got in bed and it was alot higher than the crib. There was nothing he could grab onto and it was a long way down, so if he woke he would call for me to come get him. I never worried about him falling. He wasn't much of a roller in his sleep. He is 11 now and still sleeps in the bed. (My father built the bed 50 years ago for my brother, then it was used by 3 more sisters than myself and now my son.) I personally felt getting a toddler bed would have been a waste of time and money seeing my son's progression. He was ready for one. We hyped up the idea just after his first birthday, saying that it would be his gift to the new baby, him being a big boy and big brother, and continued the mentioning of it up to the time of arrival. He loved it form the very beginning.
For my daughter's "big girl bed" (I think she was almost 2) we did about the same thing wih the hype and all, (only I wasn't expecting again) saying she was getting older and asked if she wanted a big bed like everyone else. She liked the idea. The twin went up against the wall and a rail on one side with a dresser at the foot of the bed. There was an opening towards the lower half of the bed for her to get in and out. She never left her bed at night, but I think it was a comfort to her knowing she wasn't stuck and that she could come get me if she wanted me to or just call for me to come. My kids never left their room with the rest of the house dark. They only had night lights in their rooms and the bathroom right across. Both my kids adjusted well and want loft beds now at the ages of 10 and 11. Do what you think is right and good luck!