Hi neocatcher,
As I mentioned in my last reply there is no way to quantify how long any mattress will last for any particular person but if a mattress is well inside the comfort/support range that is suitable for someone and isn’t close to the edge of the range that is too soft for someone when it is new and meets the minimum quality 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.
It’s always more realistic to think of 10 years as a maximum reasonable expectation for any mattress no matter what the quality of the materials and then treat any additional time after that as “bonus time” because after about 10 years the limiting factor in the useful life of a mattress will often be the changing needs and preferences of the person sleeping on the mattress and even if a mattress is still in good condition after a decade … a mattress that was suitable for someone 10 years earlier may not be the best “match” any longer.
With higher quality materials throughout a mattress and/or for people whose needs and preferences or physical condition or body type hasn’t changed much over 10 years then “bonus time” or even “extended bonus time” with higher quality/density materials like latex or higher density memory foam is much more likely than with materials that are in a lower quality/density range.
As I mentioned in the post I linked I have talked with them about their Green Choice mattresses. They list the quality/density of the memory foams in their descriptions so that part is easy to find out.
I couldn’t agree with this more and this is one of the reasons that I started this site and wrote much of the information that you will find on it. There are many high priced mattresses that use low quality/density materials that certainly wouldn’t be worth considering. There is more about the most important parts of the “value” of a mattress purchase in post #13 here.
3 lb memory foam is certainly a lower quality and less durable material than I would consider in layers that are more than “about an inch or so” which would be a weak link in a mattress. The density of memory foam and polyfoam is the single biggest factor in its durability and higher density memory foam and polyfoam would generally be more durable than lower density versions of the same materials.
There is more about durability in the previous post I linked but if you want some additional reading then post #5 here includes some links to more industry information about foam density and durability and if you are interested then there are also some links to more technical information about polyfoam and memory foam in post #2 here that are also very interesting but more technical reading.
I don’t make specific suggestions or recommendations about “what” to choose (either for a specific mattress or a specific manufacturer) … only “how” to choose a mattress that is the best match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) and all the other parts of your personal value equation that are most important to you (see mattress firmness/comfort levels in post #2 here) but some of the better lower budget options I’m aware of are linked in post #4 here.
Phoenix