I ordered a wool mat online from a site that makes table pads from 100% wool, and will cut to size, so I measured where it would go and ordered that size specifically.
It wasn't expensive, if I recall they are made in the USA, did not have too smooth a surface so I covered it in a couple of layers of old silk organza (which I also use for a pressing cloth).
What bothered me at first was a slight odor like old socks or wool (imagine that) when I was pressing - after a short while it faded. I don't have the website name anymore though.