I find the thinner ones much easier to cut
The thick ones are a pig to cut. If it was me I'd go with two 5mm layers - but that might work out a bit expensive. On the other hand rodipet make a 120cm sized one to fit one of their cages, which is quite large. I've had theirs and the Hugro ones and the Hugro ones are a pig to cut. But they are thicker. So - actually yes the thicker ones are probably better (and more cushioned) than two thinner ones.
Sorry that probably wasn't much help! But a couple of Hugro 100 x 40cm ones would probably do it? Without much cutting.