Hi PattyS,
As you know from the guidelines, researching your local options (first on the phone and only then with a visit) and “connecting with the experts” is one of the most important steps (step #3) in successful mattress shopping and you forgot to mention where you live 
If you let me know your city or zip I’d be happy to let you know of the better options and possibilities I’m aware of in your area.
You can read more about trying to match one mattress to another in post #2 here but unless you have enough information about both to know that all the materials and components and the design of both are close to identical or a manufacturer is familiar with how their mattresses match up to a specific model you have tested or is available for you to test in terms of “feel”, material quality, or design, the only way to know how one mattress compares to another is through your own side by side testing to compare how they “feel”. Even here, since you can’t “feel” the quality of the materials in a mattress (both low and high quality materials can feel the same), you can only make meaningful quality or value comparisons between mattresses by knowing all the details of what is inside them even if they compare well in terms of “feel” which is much more subjective.
The time you spend testing mattresses where you aren’t able to find out the specifics of what is inside them is mostly wasted (except as a very general and non specific guideline about the types of materials you tend to prefer). Because they are so widespread and well known … Tempurpedic is one of the brands that many of the manufacturers or retailers in the online memory foam list will be able to “approximate” in terms of either “feel”, quality of materials, or design or in some cases all three if you do decide to go in the direction of an online purchase.
Phoenix