I moved the crib's rails down and kept the Sims 4 mattress on the bed.
My good friend SG5150 was kind enough to teach me how to separate the mattress from the frame, so I added a separated version. Keep the one you prefer.
I am proud to say this was made in Blender.
Castaway Stories Crib As a Toddler Bed Beta.01
WIP (the DST images are blank grey)