I like old cotton bed pads for the padding, but a wool blanket is probably easier to find. I wonder which wicks moisture away better? (I already googled it, and didn't find a definitive answer....yet.)
I used those silver pads for years, and while they are great for production work (you can slide garments easily on & off the board), they do tend to reflect moisture back up to the fabric. Fine if you have an iron that toggles between steam and dry, like a gravity-fed iron. Not so good for typical home iron.
Cotton duck is best for tailoring, IMHO, but many of my co-workers made board covers from upholstery weight cottons. Polished cotton was slick and absorbent. Fun to experiment.
I'm with sdBev on the elastic board covers. I do exactly what she does. The padding condenses with use, so adding another layer just makes the board better.