I think it was my post you’re referring to, and the original link returns a 404 now. It seems it’s now discontinued, which is prolly why Sports Direct were doing them cheap.
I’ve just done a search, and the only place I can find one is here:
http://www.cnfoutdoors.co.uk/gelert-xpedition-xl-10cm-self-inflating-mattress?gclid=CIS1ipy5lcYCFWzMtAodjjsKqw
Not as cheap, but it’s the only source, grab one quick! I spent four days sleeping on mine at the IoW Festival, using a £19 Aldi mummy-type sleeping bag and a Wilco cotton bag liner, and I was really comfortable, the extra thickness you can add just by spending a couple of minutes blowing into it makes a big difference. If it’s a bit hard blown right up, it’s easy to let a bit of air out.
After four days, I opened both valves at the bottom, and it wouldn’t deflate! I had to roll it a bit at a time kneeling on it to get the air out!
