I’ve got a 10cm self inflating mat, that can be inflated quite a bit more with a few big puffs, can’t remember the make, but mine was an end-of-line anyway, cost me £17 instead of £70, and the extra thickness that it gives makes a huge difference as regards comfort and insulation.
It is heavy, but fine for camping close to the car, or at a festival, where you can just strap it to a large-ish trolley then wrap cling film around everything to keep it all steady.
I camped down in Devon for nine nights using it in October, with a £19 Aldi sleeping bag, and I was perfectly comfy, really nice and toasty, so I’d replace it with something as close in thickness as possible if it got damaged, it’s only let-down, (ha!) is that it’s only a single.
But it was bloody cheap!