If its due bitter Steve, ie under -10C, I'd take some CCF and use it to boost the UQ. Car windscreen reflector material works well. Not quite as warm as 3/8" CCF mats but its softer, lighter and is comfier between the layers. Like that, you'll be fine dude IME.
My local shop (QD superstore in Orton) has some 1.5m x 1.5m blankets of the stuff for £2.99.
My local shop (QD superstore in Orton) has some 1.5m x 1.5m blankets of the stuff for £2.99.