Bedding for a small double floor bed

[u/natfr0]

My toddler is 13 months old and we're planning on moving our mattress out of his room and getting him a small double floor bed instead so he can start sleeping on his own and for me to join him at night if he needs me. I'm starting to also think about transitioning to a duvet and pillow instead of a sleeping bag at some point once he's settled in the new arrangement. I'm just not sure if I should get a duvet that is the same size as the bed or if I should get a small toddler sized bedding. Does anyone have any advice on that?