Hi somecows,
There is a whole community of people who prefer to sleep on hammocks (see here) and another community of people who sleep directly on the ground or on a wooden or carpeted floor (see the links in post #2 here) and there are some cultures that tend to prefer very firm sleeping surfaces that would be much too firm for most people in other cultures to sleep well on (see post #2 here).
The bottom line is that it’s not as important “why” it works as “that” it works and personal experience always trumps “theory” although your comment about waking up “pretty pain free” may indicate that there is still room for improvement.
There is also more information in post #2 here about the different ways to choose a suitable mattress that is the best “match” for you in terms of PPP that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for that are involved in each of them.
Buying a mattress that you haven’t tested in person (or even that you have) that provides you with good options after a purchase to make changes to the comfort and support of the mattress by rearranging layers or exchanging individual layers or the mattress itself or that has a good return/refund policy has much less risk and gives you the chance to test a mattress in “real life” with little risk which in the end is the only way to know for certain whether it will be a good match for you.
If you decide that you want to purchase a mattress other than your air mattress then if you’ve done all the research that you can the time will always come when further research reaches a point of diminishing returns and the only way you will know for sure whether a particular mattress will work well for you is to hold your breath, grit your teeth, and pull the trigger on the one that you believe would be the best match for all your criteria … and sleep on it in person .
Phoenix