When searching for a baby SleepSack (or wearable blanket) that would be very warm in the winter and was made of only natural materials, I came across Snugbags. The company is based in New Zealand, so shipping might take longer than what many people are used to if you are ordering from a well known online US based store, but I found the wait well worth it. We have been using this SleepSack for our baby most of the winter so far. It keeps her warm and is so cozy! I am hoping it will last next winter as well. Here's some info on the Sack: