I have always done my best to keep shipping/packaging costs down, yet keeping the quality and strength the best I can without paying too much.
Over the years I have moved from using 12″ record mailers with stiffeners, to smaller A4 size cardboard envelopes with stiffeners. The newer envelopes I am fading in over the coming weeks are made from corugated cardboard, and the artwork is taped inside a thick plastic bag, taped to the centre of a thick 6mm thick cardboard stiffener. The packets when packed are now as stff as a piece of wood. This makes the parcel a lot stronger and weighing the same as before.
There was nothing wrong wth my packaging as any returns I got sent back always showed up in perfect condition, just as they left me. I have not had to repost any orders because the artwork arrived damaged, I just upgraded the packing to make sure all artwork carries on arriving in mint condition, especally when parcels were in the post for longer periods during the virus peak a couple of months ago.
I cannot do anything about shipping costs, they are increasing constantly, I often lose money on shipping charges to make a sale more affordable to you. Free sheets are always added to all orders, often more free sheets added than the number of sheets ordered. The free sheets are to help offset the postage costs. If you sell those free sheets at later date you should get all your postage costs back.