Hi Thinkink,
The most important factor in the durability of a mattress is the quality and durability of the materials inside it … particularly in the upper layers which are the weakest link of most mattresses. There is more 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.
While the two mattresses you are considering have different designs and one is softer than the other (the Aria is comparable to the Tempurpedic Cloud Supreme and the Dreamfoam has a little thicker memory foam layers and is comparable to the Tempurpedic Cloud Luxe) … they both use 4 lb memory foam on top of 5 lb memory foam in their comfort layers so in terms of durability they would be quite similar for most people.
The Aria has a higher density 2.0 lb base foam and the Dreamfoam uses a 1.5 lb base foam and while for most people this would make little difference in real life … for those that are in higher weight ranges (higher than the low 200’s or so) and are more likely to compress the support core of the mattress “through” the comfort layers more deeply then the higher density base foam could make some difference in terms of durability.
NOTE ADDED JAN, 2016: They have now introduced their new simplified choice mattress which has replaced their previous models and have also become a member of this site.
While there is no way to quantify how long any mattress will last for any particular 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 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 about 10 years as a maximum reasonable expectation for any mattress no matter what the quality or durability 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.
Phoenix