I used a dehumidifier over winter which helped greatly with the insulation issues but I'm now looking at ways I can make the bedroom more insulated before next winter.
I've made a small hole to see what's behind.
The room has an 8 ft long window above stripped wood cladding and some water proof sheeting on the outside and plasterboard backed with 1cm of polystyrene on the inside. There is a ventilation gap in between.
Should I look to remove the old plasterboard and replace with something that has a much deeper insulation material? Maybe 25mm or 50mm polystyrene or should I add an additional layer?