The best lumbar support I’ve found is Fitterfirst’s ProActive Disc. The primary purpose of this inflatable disc is to give a “Swiss Ball” experience to ordinary chairs. It also works very well as a highly-portable lumbar support for flying and driving. The device was designed by this specialty shop. It’s made by Cascade Designs and has the same wonderful oversized valve used on the Therm-a-Rest mattress pads.
The way to use the disc is to fully inflate it, position the pad where you want it, and crack the valve until it’s deflated to the desired level. It’s pricey but should last forever if treated well. If you do happen to mistreat the pad, you can use the Cascade Designs repair kits to fix it. I also use it when going to events at a stadium for cushioning and to boost my height a bit (yes — I was that guy sitting in front of you). One option that’s a bit less expensive is the Ledraplastic Overball: a little ball marketed as a play toy about 20 years ago.
The balls inflate to a diameter of 7 to 9 inches; they’re springy and remarkably strong. Some Pilates instructors started using them as a substitute for Joe’s Magic Circle. The Pilates Mini Ball workout is a classic (here’s a sample). Colleen Craig’s “Strength Training on the Ball” uses a mini ball in tandem with a Swiss Ball for multi-directional destabilization — a fantastic strength/balance program in a book.
After getting noticed, many different manufacturers are making their own balls now: the FitBall Mini, the Fitterfirst Mini Ball, the Franklin Air Ball, and even Leslee Bender’s Bender Ball (promoted on infomercials). All of these little balls are are well-made; they are interchangeable. If you hurt after a flight, lying on the floor with an Overball (or one of its imitators) in the small of your back is tremendously relaxing.