You are fortunate in the USA - your postcard postage rates are very reasonable.
I have been sending and receiving postcards in the APUG postcard exchange for years. Most make it fine through the mail without damage, although sometimes the "damage" that occurs occasionally actually adds to the character (IMHO).
I live very near the Canada USA border, so I print to the USPS postcard size requirements (4" x 6" is best), and mail all my cards addressed to non-Canadian addressees from the US.
I have used the Ilford postcard paper, which is on the heavier "Portfolio" stock, but mostly I use regular RC stock. The secret to improving the durability of the postcard is to use adhesive labels on the back of the card which cover a substantial portion of it. That also gives you either a better surface to write on, or the opportunity to print the information using a computer printer.