You've gotten great advice here. I would just add: make sure you have *wool* socks to wear in those boots. You can also add toe warmers if needed for Chicago - if you place a hand warmer on the top of your foot, it warms the blood heading to the toes. Fleece/sherling insoles can also elevate a non-insulated boot in a major way. And perhaps you could order a puffer when you're stateside - as others have mentioned, Lands End, Eddie Bauer, and Athleta are all good options.
