I actually have 2 large mats [bought on sale years ago] for squaring up quilts. I only use them on the bigger projects. I store them under my bed so they won't warp or look unsightly. I have flat tile flooring in the bedroom./ Actually, that is also where I store my big roll of batting too.
I use my 17" x 24" mat on top of my cutting table for most everything except the big stuff, as it is the right height for me.
ali