Hi tarpon21,
I’m not sure which specific mattress you are referring to but my comment was meant generically in reference to a 1.8 lb polyfoam base layer. It’s a good quality and durable material but there are also some manufacturers that use higher density base layers although they may also be more costly. There isn’t a way to attach a specific “number” of years to the durability of a mattress because there are too many factors involved and durability and the useful life of a mattress is relative to each person (see post #4 here). When I look at mattresses though I look for weak links that are more likely to soften and break down prematurely over time. The most important part of a mattress’ durability is in the upper 3" to 6" or so of a mattress that are compressed more and subject to wear more than the deeper layers. Higher weights and larger body types will sink down more and need more durable materials in the upper layers than lower weights. Of course durability is only one part of a successful purchase because no matter how durable a mattress may be if it’s not suitable for you in terms of PPP and you couldn’t sleep on it comfortably then it wouldn’t make any difference how durable it was so durability and suitability and price and all the other parts of your personal value equation are all important parts of a mattress purchase.
Mattress sagging isn’t as big an issue as the softening of the foam in the upper layers (with or without sagging). Foam softening leads to the loss of comfort and/or support and the need to replace a mattress and if there isn’t a visible impression (with you off the mattress) that is deeper than the warranty exclusion then foam softening and the loss of comfort and support isn’t covered by a warranty.
The good news though is that none of the mattresses you’ve mentioned have any obvious weak links or layers that are more likely to soften or break down prematurely.
I have no idea if Sleep Warehouse will give you a discount but it certainly doesn’t hurt to ask.
You need to tale with them just like you are doing here and tell them the criteria that are most important to you. One of the most important things is to talk with them about how well each of their mattresses you are considering may match your body type and sleeping positions and preferences in terms of PPP. If you can’t test a mattress in person then you are dependent on using their guidance and the “averages” of their customers along with any relevant information you can provide about any local testing you have done so that they can help you decide on which of their mattresses have the best odds of being suitable for you. I would also want to make sure I knew the specifics of all the layers in any mattress I was considering if it isn’t listed on their website so you can make more meaningful comparisons and identify any potential weak links (although none of them are likely to have any significant weak links). I would also want to know the specifics of their return policy or any other options they provide and the costs involved in case you make a choice that isn’t suitable for you. In other words you would want to know all the things that were the most important parts of your personal value equation.
In some cases they may also be able to suggest a Tempurpedic model or other major brand that is widely available that is similar to a mattress you are considering so you can use it as a guideline and decide if the mattress is suitable for you based on your own personal testing and experience.
Phoenix