I have Olfa mats and like them, but sometimes the green color matches the fabric too closely. I recently bought one of these mats -
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1. It was shipped flat, so no worries there. The two sides are both useful, with pink and blue so you can always get something that doesn't match the fabric you're cutting, and it's extra thick. The only downside is that the size is not what you expect - the grid is only 23x35, not 24x36 as advertised. I just have to remember when measuring yardage against it that I'm measuring 35" at a time, not 36".
The first mat I bought was grey with orange lines, Fiskar's I think. I had difficulty seeing those lines.