condensation Vs vents and cold rooms

I seem to have a problem with condensation in the bedroom.

Double glazed windows no vents

The walls are cold, cannot afford to dry line yet.

I tend to leave the top window open on the first opening so open a crack but still fairly secure.

I know I could cut one or two vents in the room but OH is cold blooded at the best of times without me adding more holes in outside walls.

Any cheap / reasonable suggestions.

Small dehumidifier for bedroom if this is only room affected.

you require ventilation
you give of water vapour when you breath, cook, shower, dry clothes etc
this condenses on the coldest surface - in your case your windows
leave the window open when you're in the room
job done