Hi jd,
That’s encouraging news and as Steven mentioned even a small amount of sag can make a significant difference in both alignment and weight distribution on a mattress.
I generally advocate a “step by step” approach so that it’s easier to isolate the main cause of any symptoms on a mattress or at least the one that is the “primary” culprit. In this case with the sag you mentioned, testing the mattress on the floor would be the most effective way to determine the effect of your sagging base. While it can be a “pain” to do some of the detective work that can help … it’s easier and less frustrating than making more “haphazard” changes that all seem to fail because they don’t address the main cause of a sleeping issue.
If your “floor experience” points to the bedframe being the main or most significant issue … then either a new bedframe or adding support under the center support beam of your bedframe would be the most logical step and then from that point you could address any other issues that may also be affecting you or make other fine tuning adjustments that would help. In most cases it’s important that the center support beam in your bedframe has at least a couple of legs underneath it to the floor to prevent it from sagging. You can also add additional support to the center of your bedframe or raise the center of your bedframe with adjustable legs like these or like these or with additional slats which are supported to the floor such as these. Other than that it would be a matter of replacing the platform bed itself with something stronger and less prone to sagging that was better supported in the center … with a steel bedframe and foundation that was more supportive and more rigid in the center … or with a free standing wire grid type bedframe/foundation combination such as some of the ones listed in the foundation thread here (although these are not my favorite long term option for an all latex mattress for the reasons mentioned in post #10 here).
Once the support under the mattress is “fixed” then you would have a better frame of reference and be in a much better position to assess the effect of any other changes or fine tuning that would also be helpful in moving even closer towards your “ideal”.
Phoenix