Deep-Cut Studios have made up some more extra-large mats for me. The extra-large Plains design mat is just over 8' by 6' (2400mm by 1800mm approximate).
I also now have the same Plains design with a very subtle 15cm cross grid or a 20cm cross grid. Instead of a formal grid with solid lines, these have a very subtle "cross" grid, indicated solely by crosses at the corner of the squares; you can just make them out in the (very poor) photo, below.
Deep-Cut mats are printed on a thin, light cloth which can be washed, ironed, and folded or rolled away for storage. Hills can be placed on top or even, if shallow, underneath. I regularly export worldwide, postage to the U.S. on these is around £15.00 GBP.
These mats (along with many other designs) can be found in the BigRedBatShop.
There are some mats and other sale items.