Go to Morrisons and buy a double duvet. I did when I forgot my bag and mat on a winter trip (sleeping on the floor in a hut) and I was warmer than everyone else - bit bulky but only a tenner and you don't need a mat if you roll yourself up in it.
Also highly recommended for sleeping in the car or car camping.
I good humouredly thought him climbing inside a dead camel for shelter from the desert perhaps wasn't so helpful given the ability of camels to survive in the desert.
Decathlon will probably be your best bet if you don't want to spend to much. No one uses season ratings anymore as nobody had much idea what they meant in the first place!
I always take a duvet car camping, squashing it for a short time ,between sleeps, in a dry bag does not seem to damage it, and it does not take up much room at all in the car whilst travelling.