I have a multiple listing with various sizes of bags. One is much large and heavier so will cost more to post than the others. At the moment the postage is the same for every item but I wondered whether there was a way in a multiple item listing to have different postage prices for different items. The rest will all be large letters but this bag would need to be a small parcel. Is there any way to do this or should I just add the extra postage to the item cost.