For postage I use the 8.00 flat rate mailers you can get from the post office for free. You have to order them online but they deliver them to your house for free too. That way, no matter what they weigh or where you are sending in the US, they are $8. It’s the padded flat rate envelope EP14PE. 9.5 x 12.5
https://store.usps.com/store/product...elope-P_EP14PE