What I did was:
– cut off the shorter, knotted edges of the rugs, and then zigzagged them to prevent fraying.
– then I sewed two rugs together, pressed and steamed the seam and then strengthened the seams with topstitching.
– I used IKEA’s sturdier cotton ‘Minna’ fabric for the back with an overlapping seam and simple velcro closure.
– I kept the length of the rugs and folded under, so it looks good from the sides too! (= therefore the fabric of the back is shorter than the front)
– For the stuffing I simply recycled the old mattresses (complete with cover and all) and made the new cover a bit smaller (both in length and width) for a nice, firm look.