I don't work in an office, I am lucky enough to work from home, so fortunately I don't have to worry about how I'm dressed for work... However I often am sitting still and barely moving for anywhere between 12 to 18 hours straight (just getting up to feed the pets, make a cup of tea, and go to the bathroom, basically... Which I know, is way too much sitting...I know)
My room temperature is often around 13°. Which is quite cold. I don't think many people have indoor temperatures that low. And when you're sitting, and not moving, the cold really gets to you. And I'm going to have to assume that when you're working in office clothes, it's even worse.
A hot water bottle on your feet does wonders, especially if you can cover it with a small throw / blanket to keep the heat from escaping.
Another hot water bottle perhaps in your lap perhaps with another throw over your lap also does wonders.
Personally I don't think you can go wrong with hot water bottles.
I doubt that you can dress with a scarf or a warm hat or something like that if you're in an office, but that really does help keep the warmth in.
If at all possible and it may not be, you should try to get up every 45 minutes or so and do a brisk walk or some type of brisk exercise. If you are allowed bathroom breaks that frequently, don't go to the closest one, if there's another floor two or three floors up, go there. Move. Movement helps. Sitting still makes you freezing.
It's a minor thing but drinking warm drinks does help, warm cups of soup, warm tea warm coffee warm hot chocolate warm cider etc. Of course that might mean that you'll end up having to go to the bathroom and awful lot but, you do get to move then.
The warm drinks may not do a lot but they do help to keep your core temperature higher. And if you can, try to avoid cold drinks as that'll chill you down.
I hope some of this helps