I bought a lightweight camping mat from Lidl last year, and they are back in stock again.
I've used this quite a bit now, including over winter, and I am impressed, so I snapped up another two - a bargain at £17.99. Weight 508g, pack down small, and they are really comfy. The outer two tubes are slightly larger diameter so I find that I don't have a tendency to roll off the mat. Recommended if you are on a budget.
Note - this is NOT the Crivit self inflating mat that is on their website right now.