A gal in a local sewing group had this little wool mat (12" x 12" x 1/4" thick) for her iron.  Yes, it is thin, but it didn't heat up the table.  The price is fabulous $13.50 plus shipping.  I ordered myself one today.  She shared hers with me while we sewed, and it worked really well.   I guess one could get two, for more thickness, and attach them together.

https://www.etsy.com/listing/765497249/insoles-100-pure-wool-felt-cut-to-fit?click_key=e3e469a036ae0f28a75f78d399ec5d40b3c25796:765497249&click_sum=8d9c694e&####

Just be careful when you are ironing cotton fabric with iron on cotton setting; move  your iron quickly. 

My wool felt pad now has a few brown scorch marks.  Nothing drastic but I guess those marks show I am slowing down in my old age.

if you use steam be careful tho, I've had steam go through my thick one.  I'm guessing it would go thru a thin one quickly.

You are so right, Dee!  I used my mat on the kitchen table, and when I quit for the day, there was a fair amount of condensation under the mat.  I really could have warped the table surface if I had left it there longer. 

Sue in IL