I use Priority Envelopes, they arrive much faster. Fran in Spain received one only 4 days after I mailed it one time.Also, I have NEVER had one of these come up missing. I was told by a local Postmaster they are sent out with the Registered Mail.
I believe the price is $6 and you can pack as much as you want into it. USPS provides the envelope, you just need to fill out the customs form etc....