You should look into http://www.freshbooks.com/ I use this for my invoicing needs, and they do offer to send paper invoice as you describe. They have awesome customer service and the people behind the company are great too, I think they send a cake to a randomly selected new subscriber every month.
I have tried Freshbooks. Nice service, but it only does the invoicing part, leaving me to do the packing list + labelling myself. The service I want/should program myself does both automatically.
Maybe I'm not understanding you correctly but Freshbooks has a service that will print out the invoice, pack it, and send a physical envelope to the client on your behalf. You don't need label or pack, they will do this for you for an additional charge.
