Hi Jaclync,
I took a quick look but I didn’t see anywhere that I could find even the partial specs of the materials in your mattress that may have been available at the time. If I am looking for this type of historical information the method I generally use is to find a retailer that may have carried them at the time (probably around 2007) and that lists the layers in their Stearns & Foster mattresses and then look through their sites on the wayback machine here to see if you can find a listing for this particular mattress. You won’t find out any information about the firmness level of each layer or the density of the foam because Stearns & Foster doesn’t disclose this information then or now so in the best case all you would be able to find out would be the type of material and the thickness of each layer.
I’m curious though about what you were hoping to find out and how knowing the layers in the mattress would benefit you because even in the best case if you find a historical website that tells you the type and thickness of the layers it won’t be particularly useful in terms of replacing the materials with similar layers.
If you are doing mattress surgery then post #2 here may also be helpful.
Phoenix