Hi R-10,
While things like comfort, firmness, and PPP (Posture and alignment, Pressure relief, and your Personal preferences) can be much more subjective … the durability and useful life of a mattress is more dependent on more objective factors that you can verify for yourself.
All manufacturers have access to the same or similar materials that they can use in their mattresses so the most important factor in assessing the quality and durability of a mattress isn’t by knowing the name of the manufacturer but by knowing the type and quality/density of the materials inside it.
While there is no way to quantify how long any mattress will last for a specific person or predict exactly when you will decide to replace it because it is no longer suitable or comfortable for you (because this is the only real measure of durability or the useful life of a mattress that really matters) because there are too many unknowns and variables involved that are unique to each person … if a mattress is well inside a suitable comfort/support range and isn’t close to the edge of being too soft when it is new (see post #2 here) and you have confirmed that it meets the minimum quality/durability specs that are suggested in the guidelines here then it would be reasonable to expect a useful lifetime in the range of 7 - 10 years and with higher quality and more durable materials like latex or higher density memory foam or polyfoam (in the comfort layers especially) it would likely be in the higher end of the range or even longer and the chances that you would have additional “bonus time” would be higher as well.
There is also more detailed information about the many variables that can affect the durability and useful life of a mattress relative to different people in post #4 here and the posts it links to.
In its simplest form … choosing the “best possible” mattress for any particular person really comes down to first finding a few knowledgeable and transparent retailers and/or manufacturers that sell the types of mattresses that you are most interested in (either locally or online) and that can provide you with all the information you need to know to make an informed choice and make meaningful comparisons between mattresses and then …
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Careful testing (hopefully using the testing guidelines in the tutorial) to make sure that a mattress is a good match for you in terms of “comfort”, firmness, and PPP … and/or that you are comfortable with the options you have available to return, exchange, or “fine tune” the mattress and any costs involved if you can’t test a mattress in person or aren’t confident that your mattress is a suitable choice.
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Checking to make sure that there are no lower quality materials or weak links in the mattress that could compromise the durability and useful life of the mattress.
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Comparing your finalists for “value” based on #1 and #2 and all the other parts of your personal value equation that are most important to you.
Phoenix