Bonnie Hunter was using a wool pressing mat on her latest Quilt Cam, Aprill 11th (I think). She says you shouldn't use Best Press or starch with them, but she uses a water misting bottle from a beauty supply store. I like to starch a lot, so that would be a drawback.
I recently bought a clapper, which is an old fashioned device for making seams stay flat. It's a heavy chunk of wood that you place over each seam as soon as you iron it. I think it works by quickly reducing the temperature. I was surprised by how well it works. My seams stay perfectly flat. Google "clapper pressing tool". They come in different sizes, and a large one costs about $25. This could be used in combination with a wool mat, too, but might be overkill if either one works well alone.
I have wondered whether felting an old wool sweater wouldn't produce a mat that would be very similar. You could sew the front, back and opened out sleeves together to get more thickness. Since it's already felted, it could be tossed in the washer and dryer, so using starch would be no problem. Old 100% sweaters are cheap at Goodwill and similar thrift stores, and sometimes they've already been felted for you. If not, you have to be sure it doesn't say "washable" because that would defeat our intent. In Texas wool sweaters are not common because of our climate, but I was able to get one some years ago for a craft project. I'm going to dig around and see if I have any large enough scrap, just to experiment.