M.B.
If he is becoming a little monkey with his climbing it is time to seriously consider another bed with some sheets/blankets from a favorite movie or theme (ie. cars Thomas the Train etc for a boy). When I was expecting my son ,I had to move my daughter from the crib to make room for him. I bought some sheets I knew she would like; put the mattress on the floor(less distance to fall out of bed until she got used to it; she never did fall out of bed though)put the sheets on it and told her this was all for her and was hers and something special as she was going to sleep like a big girl now. I will never forget the look on her face as sat in the middle of the bed pulled the sheet up to her chin and said proudly "mine". She too had been climbing in and out of her crib even with the mattress in the lowest position. Good Luck