You can use hand warmers but the best is to make sure there is no constriction on the skin - usually impossible with gloves thanks to sloppy design. An arctic explorer once said if you want warm hands your hands should fit in your mitts like a car is parked in a garage. Lots of room! One way is to get some mitts and cut off the thumb and area right around the first joints of the fingers. It would allow finger mobility and keep your hands as warm as possible if you don't use the solution below which is far superior. Remember that the mitt still goes between your thumb and fingers. That keeps its in place otherwise it will just slide up your hand away from your fingers.
This only works of course if you don't have to look at the keys....duh. I'm assuming most of you know how to type...lol. And you could always make the top out of glass to clear that little hurdle. The ambient temperature in my place was often below 10C/50F and I had to type. I'm curious as to what your temperature was. I just got a box slightly bigger than my keyboard/mouse and plopped it on top. The front of the box was cut out. I draped a blanket over it (ideally line the inside of the box with Styrofoam or other insulator so the heat from your hands and wrists is not wasted) and let the blanket drape over the front. The blanket will conform around your wrists giving a pretty good seal. Put something soft on the top of the desk, not only for comfort for your forearms but also for heat retention. You probably won't even need a heater in there as the skin radiates a surprising amount of heat. You could get some dryer ducting (about 4" in diameter) and attach that to the output fan of your PC case. That can exhaust into the box. Your hands might start to sweat! Another option for heat (say in the morning) is to use a hot water bottle. Or even just a bowl of hot water. Just make sure its not going to spill!
I've been trying to design some sort of poncho thing that would drape over the desk and around the chair. Getting in and out easily is the challenge. But that would allow one to work in perfect comfort in temperatures below freezing. It would allow people to really save on their heating bills in winter. Position the desk for sunlight if you're not using double/triple pane (which block out a LOT Of the sun's heat) windows.
If you want to be healthy, you need fresh air. And if you want to save money on heating costs, fresh air is mighty expensive. The answer is to sit right at the fresh air source for the room so your area has the best quality of air. The poncho thing would allow computer users to work in a fresh air environment almost any place on the planet.
Think about this: We have an energy source (often dirty coal or dangerous nuclear) that gives us electricity that heats an element that heats the air that heats our skin. The sun can shine right on the skin and bypass all those stages. Passive solar is the future. We just waste about 99% of it presently. Every house should be oriented to grab that free sunshine.