Long johns. More layers. Silk and wool. Drink warm liquids (hot tea, hot chocolate, warm chicken broth)

Is your chair a mesh fabric? Drape a blanket over the chair and sit on that, so no air is coming through to your back or seat. Since you can’t wear a hat (are you sure you can’t wear a beanie?), try covering your head in at least a handkerchief, like a biker or Hulk Hogan. Thin gloves w the finger cut out will help keep your hands warmer and you’ll still be able to work on a computer.

Do as many of these as you can and see if it helps; I’ve been cold for much of my life, and these things have helped me.