I have an Omnigrid cutting mat that is 18x30" wide. It works great for me. I don't have a dining table, but I just throw it on the floor when I need to do cutting. Sometimes I wish I had a giant-sized mat, but this size stores well. The mat is great because it is flexible and I curve it around inside my cabinet or put it behind a piece of furniture when I am not using it.
I don't think that the mat is as important per se (they all seem to be the same self-healing material), but the straight edge you will use as a cutting guide is my most welcomed tool. I would suggest one as long as your mat, and fairly thick; I have a thin, flimsy one, it is very easy for my rotary blade to skip over the edge while I am cutting. That's kinda dangerous, so I would get one that is 1/16-1/8" thick so it will press your fabric down evenly when you apply pressure and keep your blade right along the side of it. My father-in-law purchased a thick strip of plexi-glass material and glued a little bit of rubberized grip material to the back, it is a nice guide for a straight edge even without the measurements printed and it stays put.
I've got several cutting mats in different sizes by different manufacturers: omnigrid and fiskars come to mind. Any mat I've bought from Joann Fabrics has been good.
What size I need (want) has driven which brand I've bought. Love the Joann 50% off coupons!!!
BTW: I do have a blade protector. It's a really good idea when you're using a rotary cutter. I also have a metal ruler and a corner square from the hardware shop that I've used to protect me from the blade when I'm using an exacto knife. Hope this helps