My 3 month old baby is about 13 lbs, soon to be transitioning from sz 1 to sz 2 swaddlers. I have a box of 150 sz 2 swaddlers, and trying to figure out if I should get one or two more boxes of sz 2s before the amazon.com sale ends. How long do they stay in size 2s, typically? Will I need 300 or 450 of these dipes? Thanks for any help!