Hi Penguinande,
There isn’t really a way to attach a specific number of years to how long a mattress will last for any particular person because there are so many variables involved (with both the mattress and the person) that can affect how long a mattress will maintain the range of comfort and support that is suitable for any particular person before they cross the threshold from sleeping well on a mattress to “tolerating” it and eventually deciding to replace it. Having said that … 2 lb polyfoam is a durable material that is often used in heavier duty mattresses that are designed for higher weights and it will certainly last longer than the lower density polyfoam that is used in most mainstream mattresses. It’s also true that any material will last longer for lighter body types than they will for heavier body types. There is more about the factors that can affect the useful life of a mattress relative to different people in post #4 here and the posts it links to.
If a mattress is a suitable choice in terms of PPP and isn’t “on the edge” of being too soft once the initial break in period is over (typically about 30 - 90 days) then it would be reasonable to expect that it would last you for 5 years. 2 lb polyfoam would be what is often referred to as “furniture grade” foam that would be used in good quality sofas. It would be “more durable” than most of the polyfoam used in the comfort layers of mainstream mattresses (even those that are in significantly higher price ranges) but would be less durable than more premium foams such as latex but of course these are also materials that are found in higher budget ranges.
It’s usually the upper layers of a mattress that will soften and break down first and one of the additional advantages of a component mattress such as this besides just the ability to customize it for your needs and preferences is that if one of the layers softens or begins to break down before the others you can just replace a single layer instead of the complete mattress.
Overall … it would certainly be one of the most durable choices available in its budget range.
There is more about the types of foundations that I would suggest for different types of mattresses in the foundation post here but the foundations that Dreamfoam sells here and here would both be suitable choices.
Phoenix