Solution: get yourself (from your friendly neighbourhood upholstery shop) an old sample book of discontinued fabric. Trust me, they all have them, piled in heaps in dusty old cupboards. I had to buy mine, but some kinder (or possibly less-business-savvied) people will just give them away for free. Cut even-sized squares or rectangles and arrange then in a pleasing pattern (I skipped this part, as I was too much in a hurry) and then sew them all neatly together in strips (I skipped the neatly part, too), and then sew the strips together to form a large rectangle. Mine ended up rather skew, as many of my projects do when the idea of a finished product is much more appealing than the idea of a good-looking product. Never mind, I just boldly cut the edges straight. I added strips of felt on the back to add a bit of weight and prevent it from slipping around.
I consider it a prototype - one of those projects that I fully intend to make again, but properly the next time around. Actually, most of my projects are prototypes, and of course I never make them again - properly or otherwise. So my brilliant new bathroom mat is all a bit higgledy-piggledy with unintended valleys and peaks and wrinkly bits (such as I have myself), and as you can see the rectangles don't match up properly.
But my footsies are happy.