My granddaughter loves her big girl bed. However she is 4 and the 3 slats aren’t enough to support her standing and jumping and mattress. We added 2 more slats and a plywood base. Cost was around 80.  Be aware side rails are 2 pieces, and ours came with a slight crack in the headboard, thus the 3 star rating. It was easy to assemble, and our sleep innovations mattress fits well.