I wear dresses full time as well, and I'm in Mass so it gets fairly cold. I found that wearing an extra pair of knee-hi socks under my boots kept me toasty.
A few suggestions: Make your bloomers almost as long as your dresses. Sitting down and having cold knees is no fun (I learned the hard way last winter). I personally like thick flannel. It's soft and warm and you won't overheat when indoors. Pajama bottoms will work fine, just remember to lower the rise a bit so that they sit a bit below where your skirt will.
You're probably better off layering than necessarily what your skirts are made of. A nice twill or curduroy will serve you well and wash easily. You can always toss an extra slip or two. I do my skirts A-line and they're flattering and easy to work in. Consider a gored skirt for something easy and fun as well. There's no reason you can't stick to elastic. I'm a zipper girl for outer layers but sometimes use folded over lycra as a nice smooth waist for my underlayers.
I promise that you'll be much warmer in your skirts and bloomers than in pants. I was really amazed how warm I was last winter.