For the past two years I've lived two blocks from work and have had the luxury to walk to work everyday. But I've moved on to greener rental pastures and now have a 2.5 mile commute. Today was my first day trying it out with a balmy starting temp of 15 degrees and it went pretty well.

Two issues:
1) I'm terribly out of shape. The ride to work is down hill. I'm a bit nervous of getting home, but that's an issue only I can deal with.
2) My top layers kept riding up, leaving my lower back exposed. That was cold. I need help with a solution.

I'm a plus sized woman. Usually a size 20 or a 2x, with most of my weight in my belly. Even though my base layer is plus size, from REI, it isn't long enough and rides up. The sweater I had as my middle layer would have been fine, if my top layer wouldn't of kept riding up too.

So, your suggestions on long base layers and long plus sized shells please. Any help would be greatly appreciated.