I've just seen an advert for Silk Batting (over here batting is often called wadding). Never seen this before, and they say that it took a lot of sourcing.
This firm (I've used them before for silk fabric but NAYY) are having a stall at a show I'm going to in the Autumn so I thought I might order a 36" piece to collect from there (and save postage) and be temped by their fabric too.
Haven't really thought of a design - perhaps a landscape/seascape(?) but I have a couple of months to think.