We converted Olivia's crib to a toddler bed at 15 months due to the fact that she HATED her crib and we had very little success getting her to regularly sleep for long stretches in it. We then purchased a twin mattress for her at 18 months because at the time we transitioned her I was still breastfeeding and having the twin bed made this easier for me to lay with her. We really didn't have too much trouble with her getting out of the toddler bed or the twin bed. Even now at 22 months when she wakes in her room she will just sit up in her bed and start talking or crying ( depending on the mood/situation). We do have an installed baby gate at her door to keep her from wandering just in case though. While we definitely have had a few tough nights here or there overall she has done very well in both the toddler and twin bed. I will say that we are also comfortable with co-sleeping and when needed one of us will sleep next to her in her bed or she will sleep in ours when sick or just needs to.
Advice, just go for it! We did try to make a big deal out of her new space and toddler bed when we set it up. We hung out there for a bit during the day, read stories, talked about sleeping in there, and put a special snuggle toy or something in there. When the first night came we went up to her room and once there reminded her about her new bed and did our usual bedtime routine. Oh, and I did put pillows on the floor to break her fall. In the toddler bed we had two falls. One of which she didn't even wake up! In her twin bed she has also fallen/rolled out twice and also went through a short phase where she was getting out of the bed and sleeping on the pillows or rug on her floor Again, it really has been a good thing for us and not as nerve-wracking as we anticipated.