I made the switch to a BBG early, Lo had outgrown her cot and I thought she was ready. I can't remember when i did it ( even though it wasn't too long ago ,sorry pg brain! i think between 15-16 months could have been earlier ) But i do remember that it was a smooth transition with Lo falling out of her bed during naps not night sleep. I look back and wished i did it when she was around 12 months honestly.
I prepared by letting her "help" set up her new bed, put the sheets on ( i didn't wash blankets or pillow right away). She got to put her lovies in the bed too. We tried for nap and thats when she fell out the first time, Dh went in, calmed her down layed her back down and then left the room. She fell asleep right away. That night I was going to sleep on her floor but ended up not needing to ( checked on her about 20 times though). The next day was when she yet again fell out during nap time, I went in and did the same steps as DH.No problems after that.
She was "allowed" to climb into her bed by herself but we taught her from the get go to NOT get out of bed, knock on the wall, call mommy or daddy then wait. In all these months we have had her get out of bed and play maybe 3 times.
HTh in any way