I agree that at least a couple extractor fans or vents are a good idea, in both the kitchen and bathroom. (And does the clothes dryer vent outside?) Look into Heat Recovery Ventilators (HRV) and Energy Recovery Ventilators (ERV) if you're worried about heat loss. I also agree that just opening the windows once a day would be pretty effective.
It could also be that you really have a condensation problem, more than a humidity problem, from insufficient insulation. Condensation happens on items that are cooler than the room's air. When there's noticeable condensation on your windows, walls, and ceilings, it's worth checking out what your insulation is like, and maybe improving it. When the condensation is on windows, there could be air leaking through, or the window could be not built for winter (purely aluminum frames, for example, conduct heat very well, so in the winter the internal window pane/frame will be much cooler than other things in your room). The windows should be at least double-pane.
If you don't mind burning stuff indoors & have some extra money, a lot of people say wood stoves dehumidify the house.