Hi Soco11,
The back issue you are describing is unfortunately very common and usually indicates that during the course of the night you are somehow becoming “misaligned”.
This could be because of changing positions (most people don’t sleep in the same position all night) and the alignment you started in was fine but the alignment for your other sleeping positions was not and your mattress is only “supportive” in one of your sleeping positions.
It could be because the “out of alignment condition” was ok at first and not enough to cause “instant pain” but only caused pain as your muscles became more relaxed over the course of the night and “parts” of you that were being “held up” by your muscles are not being held up by the mattress … again causing misalignment.
It could also be because of “mattress creep” which means that the mattress slowly allows you to sink in deeper over the course of the night. This last one is a particular characteristic of memory foam which has much more “creep” than other types of foam such as polyfoam or latex foam. This will usually “aggravate” the other two and is the reason why I personally believe that memory foam is not suitable for most people who are prone to back pain.
While an appropriate innerspring may help, whether or not it solved or helped solve the problem would depend on the type of innerspring and also what was over the innerspring. In addition to providing most of the pressure relief of your mattress, The comfort layers are part of what “holds up” or supports the lumbar area (the hips are mainly held up or supported by the mattress core) so memory foam over innersprings could well create the same problem. The best material for a support core (because it has better “progressive resistance” than any other material) is latex … particularly Dunlop latex. Your next best choice would be an innerspring. Your least best choice would be a polyfoam core (which usually has the least progressive resistance of these 3 materials).
Another name for “progressive resistance” is “support factor” which means that a higher support factor gets “firmer faster” (doesn’t let your heavier parts sink in as far) than a material with a lower support factor. Testing for the right combination of support and pressure relief along the lines of some of the guidelines on the site (such as the five steps to your perfect mattress) along with choosing materials that don’t “creep” can make a big difference with back issues that can be aggravated by sleeping out of alignment.
Zoning can also make a big difference in certain body shapes, weight distributions, or more “extreme” sleeping positions. With men in particular … zoning that is firmer under the hips and softer under the shoulders (which in men with broader shoulders in particular will allow the shoulders to sink in far enough to create correct alignment while stopping the hips from sinking in too far) can make a big difference. In the case of back sleeping though which has less pronounced “recessed areas” in the sleeping profile … zoning is not quite as important as with side sleeping although it can still certainly help with stopping the hips from sinking in too far if the materials in your mattress don’t have enough progressive resistance to do the job by themselves.
Some general guidelines are (subject to confirmation with actual field testing of mattresses) are …
For a support core
A suitable higher quality and firm polyfoam (1.8 lbs or higher with an ILD of about 36 or higher) for a smaller budget.
An appropriate innerspring (such as a firmer offset coil or a firmer pocket coil) for a slightly higher budget
Latex (particularly Dunlop latex with an ILD of 36 or higher) is best of all.
More information about the different support core materials can be found here
For a comfort layer
HR polyfoam (technically 2.5 lbs or higher but slightly lower may work as well in an ILD in the range of 19 - 24)) for a tight budget,
Latex foam (in the range of about 19 - 24 ILD with Talalay latex being preferred by most people in the comfort layer).
More information about the different comfort layers can be found here
I would avoid memory foam completely and be wary of lower quality polyfoam (less than about 2.2 lbs) in the comfort layer as it will begin to break down and lose the qualities that made it “right” in the showroom and develop depressions much sooner that latex foam.
Both of these can help keep you supported and won’t “creep” as your muscles relax or you change position over the course of the night. Of these two comfort layer materials … latex has the best support characteristics and is the most likely to “help” a mattress core keep you in alignment as you change positions over the course of the night.
The thickness of the comfort layer is also important and a rough guideline for a back sleeper is to begin with about 2" and then adjust this up or down depending on what your field testing tells you.
Hope this helps a bit. Back pain is certainly not fun … which I know from personal experience.
Phoenix