Insulating a corner bedroom, raked ceiling- very cold

[treesurg]

We live in a 1930's semi with a raked ceiling. The corner box room is freezing and there is a small amount of mould on the curved section. The internal walls were insulated with about 1cm (guesstimate) of plasterboard type material in 1990s. The windows are PVC double glazed. Can we improve the insulation here as the room is very cold?

We really want to avoid the cost of external insulation. Should we replace the internal insulation - is there better material these days for insulation? How do we insulate the curved area of the ceiling as it's loosing a lot of heat? Any other suggestions?
Thanks in advance!

 

[^woody^]

Improve the heating instead.

 

[John D v2.0]

Yes we used to have that issue in the bathroom on that curved section, as the loft wool didn't go that far into the gap. In the end we had the builder put insulation board when the roof was replaced.
We also installed one of those under bath fan assisted radiators and that made a huge difference as it could dry out properly.