I live in a little house that has a back room that is not too sealed. It actually has the back door in that room. Always cold. MY desk had to go by the door to that room because I had no room to put it any where else.
Sitting there the last 2 days I actually felt like my toes had frost bite. So I went to dollar general and got a 3.00 curtain rod, I got one that sticks out from the wall a bit so I can move the curtain easily whenever I need to open the door. I had 1 curtain panel that is a heavy one to put up there. Sitting here at my desk I already notice a huge difference.
You could even hang a thick blanket if you have one. Anything to cut down on drafts getting into your house and save on your power (heat) bill. I might keep it up all year and see if it helps with the power bill in the summer also.
As soon as I can I will be working on sealing that back room up and getting a new back door.