Most infants in the Neo Natal Unit are not even wrapped in blankets. Because of all the wires, etc..and it lets them do things faster in an emergency. Being a mother of two premie's at different times. One being the same exact size of your premie. My two never had blankets on them. When they came home, they did not like the weight of a heavy blanket on, because they were use to sleeping with no blankets. So make the blanket a light weight type and I would just do a crib one to start with because of that factor. The longer they stay in the NICU, the more they get use to sleeping with no blankets. Our first one was only a month, the second one was 4 months.