Hi there -- Thanks for your question. This is a tricky one. Based on the information you've provided, I would say that you almost certainly need to make it firmer. That said, given the number you already have it at, there is a good chance that even making it as firm as it goes will not be enough. If this happens, it would be because the upper comfort layers above the air chamber have lost their resilience and supportiveness. If this has happened, and if the level of support they provide when your mattress is at its firmest is still causing you back pain, then you are most likely out of luck and will need a new mattress.

Now, it's worth noting that the one caveat here is that if by chance something about your support requirements has recently changed, then there is a chance you may need to soften up your number a little. The only situation where this could be the case is if a) you recently switched from stomach sleeping to back or side sleeping, or from back sleeping to side sleeping, b) you recently gained or lost a significant amount of weight (eg, 25 lbs or more), c) you incurred some kind of injury to your spine, or the like. However, as long as none of those is the case, my original instinct would apply.

I hope that's helpful.