I've been using those larger air pillow bags to protect items during shipping. Luckily I get them free from my day job (Staples uses them to pack office supplies). It's not much help, but air is lighter than paper and every ounce helps!
Also, depending on how you pack and what product you sold, flat rate boxes can end up being a bargain. Nested mixing bowls get pretty heavy, but fit in a large flat rate box.