I put some foil behind the radiator to reflect radiant heat rather than warming the wall. Also a small shelf to stop the heat going behind the curtains (in the long run we will put up thicker lined curtains). The final expense was laying a thick wool carpet with a decent underlay. While this only has a small effect on the overall insulation it does make it feel a lot warmer underfoot.
The room is now complete and as I said it will take years to cover the costs it does make a huge difference so the room never feels as cold as it used to so it will get used more often. And as someone once said to me how long does it take for a new kitchen to pay for itself.