Look into the Freemie cups as well - I use mine with a Medela pump. You place them inside of your bra and connect to the tubing, and can pump hands-free (and cord-free with the Medela's battery pack). They're hard plastic and add a few cup sizes, so it isn't invisible, but much more so than horns. i use them while driving, eating lunch, and can pump openly in front of coworkers without anyone seeing anything.