For the mat around the toilet, you could sketch out the size you need and use a little shaping around the corners and in a U shape. As I was describing it below, I realized you'd shape it like you do the neckline and shoulders of a sweater - the 'shoulders' would be the 'legs' that go around the sides of the toilet.
Start at the wide edge, inc at the ends for a few rows (either every row or every other one) then knit straight for several inches. Mark off the center stitches for the width you need, then work across one 'leg' to the center, BO and work the other leg. Do the shaping every other row at the bound off stitch edges, probably for 2 or 3 times each side, and work the legs until they're the length you need.
And I agree with Jan, both of these would be better in cotton.