I personally have always used generic mats with D&D/Pathfinder, as they tend to be the perfect size, and they have square inch spaces for easy reference of movement. We obviously don't restrict ourselves TO the spaces, as Frostgrave is not intended to play on spaces, but I like to use it for strategic reference. Makes the battlefield like a chess board. There are plenty of these mats that are 2x3 feet long, and don't have any terrain on it so that you may use any ruins. When I play on this, it tends to be roughly an hour and a half, but that is because I like to chat with my opponent. Have fun!
Thank you,
Like Clockwork