Mountain Horse makes a fabulous pair of winter tall boots - fleece lined and such.
Layers, layers, layers is all I have to say. Yesterday I wore a thermal shirt, loose sweater, wool pull-over, and then a hoodie over the top and I was fine in 19-20 F weather with wind and snow (my jacket recently went caput and I'm waiting for my new one to be shipped).
Also, ever seen those ThermaCare heat patches for people with sore/stiff backs? Get the 8 hour ones and use them, they really help a lot.
"Always be yourself. Unless you can be a unicorn. Then, always be a unicorn."