"Diff. level and drain are 14mm Hex."
Excellent, I couldn't remember.
Ikea do a fold up kids playmate, about £15 I think. It's twice the width of mechanic mats, has a wipe clean surface that's easier to slide on. Mine is a year old, seen some hard use, still not ripped it, when I eventually do I can gaffa tape it. I only use the rubber one now when I'm welding underneath or, going to a rellie to work on their car.
One last thing, if you're worried about spilling oil, get some cat litter from Aldi or Lidl. Under 2 quid for a big bag. Works better than granules or spill kits. Pour it round the spill, fill it in, brush it up, repeat. You can crush it into dust if you have to. If it's a concrete surface, or monoblock, a quick squirt of brake cleaner cleans it like new. From experience though, sticking a piece of cardboard down first is the best option. I do keep a 2l ice cream tub filled with the stuff in the corner with my extinguisher though, just in case.