You seem to have the worst of two worlds, Myhouse. Cold walls and surfaces, and a lot of water vapour generated.
Definitely insulate as much as you can. Bay windows, incidentally, are very prone to condensation. Usually a cold spot below the window, with hardly any air movement to clear the vapour. Almost stagnant air.
You have a gas fire, so I guess a gas cooker as well. Burning gas produces loads of water. If you don't have an extractor over the cooker, it is essential. Not a filter one, but something that gets rid of the steam to the outside.
Clothes drying is a big problem too. A tumble dryer would help a lot.
Also, do have an extractor fan fitted in the bathroom... vented to outside.
Even in a well insulated new house, you are producing too much water vapour. You'll notice a big difference if you can deal with it.