I use a Tech Tools (TT) cutting mat, I use 2 to cover most of my work desk, one is 12 x 18, and the larger is 18 x 24, this gives me a surface area of 18 inches by 36 inches, plus the about 1/2 inch boarder on each mat. The TT mats can be found in the USA at Hobby Lobby stores. Friskas and Olfa both also sell mats, check the sewing section.
Thanks. I was looking at some on Amazon. Many of the reviews were bad saying they smell and do not self heal. I found one from Newbraug with good reviews. Has a layer of pvc in the middle to prevent cut through.