Some use the pads from the Dollar Store that have the newsprint weight paper that is used for paper piecing. It's about 8 x 12 or bigger. You would have to tape the sheets together. It is a one time use product.
I like the idea of using freezer paper. You could cut out your designs, stitch right along the edge of the paper and just move it to the next area. I would do it for the whole width of the fabric, which is pretty simple since it comes in a roll. What kind of pattern are you doing?