Hi retrokick,
The first thing I would suggest is to step back a little and start again at square one by reading post #1 here and the information it links to. This will give you a new set of eyes to look at choosing a mattress and perhaps most important it will help you eliminate the worst choices including every mattress you mentioned and the other major brands or mattresses where you don’t know the details of what is inside them.
Lower quality materials and foam in the upper comfort layers of a mattress … whether they are in a pillowtop or a tight top … are the reason so many mattresses today soften much too quickly and the loss of comfort and support that comes from the softening of lower quality foams is not covered by warranty until it actually leaves a permanent impression that is deeper than the warranty exclusion which is not the norm (which is why warranties have little to do with how long a mattress will last).
A mattress is only as good as the quality of the materials that are in them and the material quality in the major brands can’t compete with the better smaller independent manufacturers that are either sold factory direct or through smaller sleep shops no matter what price range you are looking at. As a single example you can see the layering here of the Coral Bay you were mentioning and all of the layers are either low quality (the 2.5 lb memory foam and the polycore base layer which is 1.5 lbs) or medium quality (the 4 lb memory foam) and these materials don’t belong in a mattress in this price range.
Once you have read the information in the post I linked you will be in a much better position to focus on better choices and you will also know the value of dealing with retailers who are able to tell you the quality of every layer in a mattress you are considering so that you can make more meaningful comparisons. Without this … quality is just a marketing word that retailers throw around that has no substance or meaning behind it.
The better options and possibilities in the Detroit area that I’m aware of are listed in post #2 here.
The Mattress & Futon Shoppe doesn’t have a single mattress listed on their site that I would seriously consider or that you will be able to find out any meaningful information about what is in them (which means that both you and the retailer would have no idea of their real quality or value).
So I would read or scan some of the basic information I linked to so you can better recognize the salespeople and retailers who really do understand what makes a good mattress and who already know what you would otherwise have to learn and are willing to use their knowledge to educate you about how to make a great quality/value choice.
Phoenix