Hi Boston124,
I would be very cautious about using other people’s reviews or experiences on a mattress (either positive or negative) as a reliable source of information or guidance about how suitable a mattress may be for you or the durability of a mattress (especially if they are based on the “brand” of a mattress rather than the specific materials in a particular mattress). In many if not most cases they can be more misleading than helpful because a mattress that would be a perfect choice for one person may be completely unsuitable for someone else to sleep on or vice versa (see post #13 here).
Most manufacturers (including Therapedic) make a wide range of mattresses from lower quality and less durable to higher quality and more durable and outside of “comfort” and PPP (Posture and alignment, Pressure relief, and Personal preferences) in terms or quality and durability a mattress is only as good as it’s construction and the quality of the materials inside it regardless of the name of the manufacturer on the label.
The “weakest link” in a mattress in terms of durability is normally in the upper layers (the top 3" - 6" of the mattress) that are compressed more deeply when you sleep on it and not generally in the deeper support layers so the firmer bottom layers of a mattress will have more effect on feel and performance than they will on durability for most people. Higher weights will compress the top layers more deeply and will compress the deeper layers more so in cases where the top layers are thinner and the support core will also be more compressed “through” the upper layers then the density of the support core can also play a bigger role in durability than they would for lighter weights or with thicker comfort layers. There is more about the factors that can affect the durability and useful life of a mattress relative to different people (with different weight ranges and sleeping styles) in post #2 here and the posts it links to.
If you are in a more “average” weight range then it wouldn’t make a significant difference (although it would make “some”) but if you are in a higher weight range then it would make more of a difference.
The post I linked in my earlier reply (post #13 here) can help you make more meaningful comparisons between mattresses and help you decide which one would be “better for you” regardless of whether it would be a better bed for anyone else.
I’m not sure if you have a box spring (which has actual springs inside it that flex under pressure) or a foundation (which is more rigid and has little to no flex) but the mattresses you are looking at are designed to work best on a rigid foundation with little to no flex. If you have a foundation that is still completely flat with no sagging and it has a strong and evenly supportive surface (there aren’t any gaps in the support that are too large) and is strong enough to support the weight of your mattress then it would be OK to use but if you have a box spring that flexes or if your foundation isn’t flat any longer or wouldn’t be suitable for your mattress then I would replace it. There is more about the different types of support systems that are generally suitable for different types of mattresses in the foundation post here.
Phoenix