Hi Th3Drizzle,
That’s a much more complex question than you may realize because it depends on how you define “quality” (see post #4 here). There is also more about the different density ranges for polyfoam used in support cores in this article and in comfort layers in this article.
If you are speaking strictly in terms of durability though… then the density of polyfoam is the single biggest factor that determines the durability of polyfoam so a 1.5 lb density polyfoam would generally be more durable than 1.2 lb polyfoam but less durable than a 2 lb density polyfoam which in turn would be less durable than 2.5 lb polyfoam for example but this is only about the durability of a single layer or component and there are many other variables that determine the durability and useful life of a mattress as a whole including whether a particular layer is being used as a comfort layer or as a support layer. There is much more about all the many variables that can affect the durability and useful life of a mattress relative to different types of people in post #4 here and the posts it links to.
For the most part … the weakest link in a mattress in terms of durability is the quality/durability of the upper layers (the top 3" to 6" of a mattress) and the density of the base layers has a much less significant effect on the useful life of a mattress. In “real life” … for those that are in average or lower weight ranges then 1.5 lb density polyfoam (which is among the most common density base layers used by the major manufacturers in many mattresses that are in much higher budget ranges) would certainly be a durable material that would be appropriate as a support core … in lower budget ranges especially. The density of the base layers is a much better place to use lower cost and less durable materials without compromising the durability of the mattress as a whole for most people … especially if there are thicker layers of good quality and durable materials materials above it that will absorb most of the compression forces that soften and break down the materials in a mattress.
The tutorial post includes a link to the better online memory foam options that I’m aware of and any of these would be well worth considering. Dreamfoam is also an invited member of this site which means that I believe they compete well with the best in the industry in terms of their quality, value, service, and transparency. They are a great value in their budget range. Of course you can find higher quality and more durable mattresses (including some of the memory foam mattresses sold by their sister company Brooklyn Bedding) but they are also more costly and the difference in durability for most people in “average” weight ranges wouldn’t be all that significant.
There may also be other local options that you may wish to include in your research and if you let me know your city or zip code I’d be happy to let you know about any of the better local options or possibilities I’m aware of.
You can see my thoughts about buying from Costco in post #4 here but I wouldn’t buy any mattress where you aren’t able to find out the type and quality of the materials inside it so you can identify any weak links in the mattress and make more meaningful comparisons to other mattresses. Again though … there is more about the most important parts of the “value” of a mattress purchase in post #13 here that can help you compare the “value” of different mattresses relative to the criteria that are most important to you.
The bottom line though is that if the Dreamfoam is a suitable choice for you (and you can test a Tempurpedic Cloud Luxe which is similar to give you a reasonable idea of whether it would be a suitable choice for you in terms of PPP) and you aren’t in a much higher than average weight range, then it would be very reasonable to expect that it would last you longer than the 4 - 5 years that you are hoping for and that it would be a great quality/value choice in its budget range.
Phoenix