When my DS was in the NICU 16 years ago, the parents provided the blanket to cover the isolet. He didn't have one until I was released from the hospital to go buy one for him. Receiving blankets and crib quilts are too small for this purpose. I will mention, I got him a blue blanket and it gave a blue shadow on him that scared his nurses a few times.
I wish I had been a quilter when my kids were little, all I made were tied quilts that were a solid fabric on top and a contrasting backing. My grandbabies will have lots of quilts from grandma someday.