The best posture is the next posture!

Had some pro ergonomic wizards visit my place of work a million years ago and they kept saying this and it has stuck in my mind like an echo from the ancient world.

I try to switch posture regularly when I’m working. It helps.

Making sure to go on walks regularly also helps with lower back pain in my experience! Can’t speak for people who have actual conditions and such, but us regular folk, whose backs are fine, just weak due to sitting down too much, there are ways to combat it without paying an arm and a leg for fancy equipment.