Hi vegsister,
While there are too many unknowns, variables, and personal preferences involved for anyone to predict which mattress would be the best match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) based on specs or “theory at a distance” (see mattress firmness/comfort levels in post #2 here) … if your back issues are being caused or aggravated by your mattress (which seems to be somewhat likely because it goes away when you have been up for a while) the odds are high that you could find a mattress that will be a much better “match” for you.
The first place to start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that can help you with how to make the most suitable choice … and know how and why to avoid the worst ones.
There is also more about the most common “symptoms” that people may experience on a mattress in post #2 here that may help you identify why the mattresses you have chosen weren’t working well for you. The most common cause of lower back pain is an alignment issue from a mattress that either has a support core that is too soft or comfort layers (or toppers) that are too thick/soft for your body type or sleeping positions but a mattress that is too firm and doesn’t provide good support under the recessed parts of your body (such as the small of your back) can also lead to lower back pain.
The most important “requirement” for any mattress purchase regardless of any back issues is always to make sure that it provides good alignment in all your sleeping positions.
There is more about primary and secondary support and their relationship to pressure relief and firmness in post #4 here and in post #2 here that may help you visualize what good support and alignment “looks like”.
There is also more about the different ways to buy a mattress and how to minimize the risks involved in each of them if you aren’t confident that a particular mattress is a good match for you in terms of PPP in post #2 here that may also be helpful.
There is more about the different ways that one mattress can approximate or “match” another one in post #9 here. I certainly wouldn’t consider a mattress that used comparable quality materials to the Comforpedic line (the Comforpedic mattresses and other major brands tend to use lower quality materials in their comfort layers than I would be comfortable with considering … see this article) but quality ad durability aside … “feel” is the most subjective part of comparing mattresses and a mattress that “feels” the same for one person may feel very different to someone else. I also don’t know of any other manufacturer (member or otherwise) that makes a mattress that is specifically designed to feel the same as any of the Comforpedic line of mattresses so the only way to know whether another mattress feels the same to you (regardless of whether it would feel the same for someone else) would be based on your own personal testing either in “real time” or with very little elapsed time in between testing both of them (our memory of subjective comparisons such as “feel” don’t last very long).
I would keep in mind that testing mattresses based on their subjective or “showroom feel” can be among the most unreliable ways to choose a mattress and has among the lowest odds of success and I would use the testing guidelines in the tutorial post instead which will give you a much higher chance of success (see post #4 here).
I would also avoid using another mattress as a “target” (which may not even be the best match for you in the first place) and rate every mattress you consider against a common set of criteria based on the parts of your personal value equation that are most important to you.
Phoenix