Hi terry820,
There is more about the different ways that one mattress can “match” or “approximate” another one in post #9 here but it’s unlikely that you will be able to find out the specifics of the materials inside your mattress (Simmons doesn’t provide this information even on their current mattresses) and even if you did it’s unlikely that you will find another mattress that uses exactly the same design with the same components and materials so the only way to know whether another mattress would be similar would be based on your own personal testing and experience.
I would also make sure that you’ve read the mattress shopping tutorial here (either the shorter or the longer version) which has all the basic information, steps, and guidelines that can help you make the best possible choice … and know how and why to avoid the worst ones (including the major brands like Simmons or any mattress where you aren’t able to find out the type and quality of the materials inside it).
Phoenix