My trusty Karrimat stayed with me until a mishap 2 years ago when all of my kit was taken from the back of my car
As Hugh says, the Karrimat does the job, although it was bulky to carry. I bought a cheap foil backed foam mat from Cotswold, the price of these, compared to the inflatables, was nothing, plus the weight of the inflatables with many around 1.5kg and some even 2kg put me off. This mat was fine for sitting on, but not good enough for a descent night kip.
Then a colleague of mine lent me his Exped SynMat Ultralite 7 Camping Mat and this ticked all the boxes except for price. Firstly, it weighs only 460 grams and is made of a very tough material so punctures would be rare, I blew it up in under two minutes inside my tent and slept like a baby! I paid £100 for mine, which is the large as I am 6’2”. I see now they have dropped in price to around £70. The only problem I have had with it is that peat stains, which is in abundance in the Lake District, do not wash off so the mat looks grubby even when it is clean.