Mines had a duvet and pillow since about 13m he hated a sleep sack from about 9m 😂
We’ve had since 13 months but in a bed not a cot. I personally wouldn’t use a duvet in a cot x
My eldest had her first duvet & pillow when she was 23 months. I'm just going with my instincts, when my youngest is ready for a duvet & pillow, I'll know.
We did it a few months ago after she grew out of her sleep sacks. It took awhile for her to not kick the duvet off but now she stays under it all night and works well. Shes in a cot bed but still have it with all the sides up ☺️