If that's too expensive, just leave a bowl of water to evaporate in rooms where you spend the most time. Drafts are another problem. Windows and doors are the biggest offenders, with older homes the most vulnerable. Next spring you'll want to check that all your windows and doors are properly caulked. Since it's the dead of winter, let's see what we can do from the inside.
Cold air falls off the inside of a window, just like rain falls off the outside.
The cold air falls to the floor and sweeps into the room. Begin by closing your drapes. Naturally, the heavier they are the better. If you can, move your favorite chair away from any windows. Even a few feet will help.