Hi basscadet,
There is more about “matching” one mattress to another one in post #9 here but there are several others as well in the list of online memory foam suppliers here that compare their mattresses to the Tempurpedic lineup or that can help you choose which of their mattresses would be closest to the Tempurpedic mattress you are considering besides the three that you mentioned.
When you are considering an online purchase that you can’t test in person then a more detailed phone conversation is one of the most important parts of a mattress purchase so you can make sure you have all your questions answered including the ones you know to ask and the ones you may not initially realize need to be asked as well (see mattress firmness/comfort levels in post #2 here).
Firmness ratings are very subjective and can vary between manufacturers or even between different people on the same mattress so it’s much more reliable to assess the firmness of a mattress with your own personal testing or when that not possible by using a reference point of a specific mattress that both you and a manufacturer are familiar with and based on a more detailed conversation on the phone. These types of questions may not be as simple as you believe they are where a single firmness number or rating will tell you much about a mattress in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) or how firm or soft it will feel to you.
Phoenix