If the duvert is of the same brand as Suzhou silk factory, that will not be a problem and I think it is not difficult to find its stores in Shanghai. Silk duvets is expensive and usually there is sample enclosed to show what inside. It touches differently with polyester. Printemps-Shanghai, Nextage Department Store and many other big malls in Shanghai also have special zone to sell home textile. You do not worry about the quality here, perhaps the price is high, because they are all famous brands.