Could you not just die? There is a video with Janie Bryant (Mad Men's genius costume designer, and a fellow East Tennesseean, I must add) on AMC's website, and when she found the above shift at her favorite thrift shop, she grabbed it with haste.
The screen shots are a little blurry, but that maxi dress needs to be in my closet. And I don't even favor maxi dresses.
Oh, and for good measure, how about a little New Year's Eve celebrating-at-home-Don Draper?