If you want to be able to be seated next to your machine while you cut, you could do what I did and that's use a folding TV tray. It's big enough for a 12 x 18 in. cutting mat, plus when I'm not cutting, I just throw a piece of fabric over it and I have an instant ironing surface.
If I'm cutting anything bigger than that, I'm using my dining room table, I just do my best to cut as fast as I can so it's not covered in fabric for an extended period of time.