There are probably two different issues: cockpit comfort and crash protection (for the spine). Inflatable cushions no doubt provide comfort, but my guess is that they provide nothing towards crash protection. EAF cushions probably provide both, but can be awkward to get right. A motorbike back-protector should make an excellent shell to slip between my back and my chute, and provide a mount to glue some EAF where the cockpit contour makes a void under my back.