I’ve had a chronic lower back problem for years and am one of those people who have found a Wingnut bag to work best.
They carry the weight much lower on your back than a traditional pack so your whole centre of gravity is lower and there’s less leverage force going through your lumbar region too (sorry, there’s a much better description for that out there somewhere but my physics schooldays were far too long ago to remember it). Keeps it warmer too!
At one time there was a camelback with a similar style, in fact it may be better as iirc it had a horizontal bladder going into the ‘wings’.