I just had a thought on Linen.
I used to do a bit of cross stitch (it was a phase) and the material used is Linen.... as in "made from Flax" proper linen.
This probably makes it a bit easier to obtain knowing this.
For example: Pottery Linen Cloth Clay Burlap DIY Pottery Ceramics Clay Craft Pad Cloth P O8Z6 4894890002840 | eBay and Pure Linen - Ivory - 140cm
– Super Cheap Fabrics
edit - the history and manufacture of real linen is fascinating: Linen - Wikipedia