Hi ericC,
I think that there are two issues here that are both connected. The first of course is having a way to know whether the materials in the mattress have the quality, durability, “safety” and value that justifies the cost.
The second is that if you are spending that much money on a mattress … I would want to deal with people who had some knowledge of mattresses and the materials that go into it and could also be able to give you good guidance about making the best choice for you. The mattress you sleep on can have a greater effect on your overall well being than almost anything else you will buy over the next decade or more and it makes sense to me to make sure you are dealing with people who are more interested in “matching you to a mattress” than they are in just making the sale. I believe that who you buy from can be just as important as what you buy.
I think that warranties can be deceptive because most memory foams don’t develop impressions as easily as they become softer in the areas under the heavier parts of your body. This softening of material leads to the loss of comfort and support which is not covered by warranty unless it also has an impression with no weight on the mattress which is much less common. You can read more about mattress warranties here. I would always put more emphasis on knowing the materials in a mattress along with your own testing than on a warranty.
The link I mentioned in my last post includes the better possibilities I’m aware of in your area and post #12 here has a list of some of the better online memory foam retailers and manufacturers I know of which have good quality/value and can also act as a “value reference” for a local purchase.
Phoenix