After reading on the forums here how layering is key... I live in wisconsin and figured I'd see if I could convert some baby onsies... I bought a 4 pack of long sleeved onesies in the newborn size. I pinched about 1/2in on the chest and seamed a straight line. Tacked it so it would lie flat cut off the snaps and hemmed it, hemmed the sleeves and voila! I also converted an adorable pajama sleeper into jammies... once I figure out how to post a picture I'll show you guys!
