Hi Akirk70,
I think the lack of meaningful information is likely to be a combination of factors but the “source” of it is the lack of willingness on the part of many manufacturers to even tell their retail outlets so they can’t in turn tell their customers.
Kingsdown is one of the “offenders” yes and I don’t recommend them at all unless for some reason you are able to find out the specifics of their mattresses and even then you would find out that they would not compare well to many other alternatives. An example of Series 6 that Sleepy’s used to list the materials (but not the quality of the materials) is in post #13 here to give you an idea of how horribly overpriced they can be. Post #232 here has more comments about this. The are also a few instances on the forum such as post #23 here where someone cancelled an order because of what they discovered here and the retail outlet offered them a significant discount (still profitable of course) not to cancel. They are a good way to buy polyfoam (or any other materials that may be in them) at inflated prices.
I would also really want to know the details of any of the “cheaper” Shifman line which include polyfoam in the mattress (which can be seen on the law tag).
Yes these are the types of smaller manufacturers I generally recommend including in your research. Martin’s Furniture isn’t listed on the Dutch Craft site but these “retail outlet finders” are often not up to date. A forum search on “Dutch” (you can just click the link) will bring up more references about them but the basic gist of it is that they are a good option to include in your research and the odds are greater with manufacturers like this that you can find out all the layers in your mattress (in this case hopefully the “all latex” is for real but a quick look at the law tag will confirm if there are any other materials) and that the quality and value will be higher.
Martin Furniture seems to be in Murfreesboro and there may be quite a few more options if you are OK with driving 100 miles or so. There is a Nashville list in post #7 here (and I’ve added Martins to it as well … thank you) and an Atlanta list in post #2 here (with probably the best choices in the general area), a knoxville list in post #2 here, a Huntsville list in post #2 here, and a Birmingham list in post #57 here just in case you go to any of these areas in your “travels” 
I wish I could be more help in making an “exchange” selection but in the absence of meaningful information it is really just a roll of the dice. If you are able to choose a mattress which is significantly less than you paid and have a refund for any difference (instead of a full refund which of course would be best) … then a mattress which has the thinnest and firmest possible comfort layers (which would also be the least expensive) and then adding a high quality topper is also a “reasonable” option.
Phoenix