Hi need2sleep1.
The major brands such as Sealy/Stearns & Foster, Simmons, and Serta all tend to use lower quality and less durable materials in their mattresses than most of their smaller competitors that will tend to soften or break down prematurely relative to the price you pay which is why I would generally suggest avoiding all of them completely (along with the major retailers that focus on them as well) regardless of how they may feel in a showroom along with any mattress where you aren’t able to find out the type and quality/durability of the materials inside it (see the guidelines here. along with post #3 here. and post #12 here. and post #404 here.).
Tempurpedic mattresses use good quality materials but as you know they are in much higher (and mostly unjustifiable) budget ranges and for most people they certainly wouldn’t be in the best “value” range compared to many other smaller manufacturers that use similar (or in some cases better) quality materials that are in much lower budget ranges. You can read more about Tempurpedic in general in posts #1 and #2 here…
I am not very sure what is the cause of the mattress feeling firmer and more supportive in the showroom than the one that you received. The showroom models usually experience some “breaking-in” (from customer use) and would be softer rather than firmer. There are a few possiblilities to consider such as
~ you tested a firm version and received a medium or soft comfort choice. It may be worth verifying that you did not receive a softer firmness option of the same model.
~ Another consideration would be the temperature of the showroom, if when you tested the mattress the showroom was very cool it can make quite some difference in the level of comfort you experience. The feel of memory foam can vary dramatically as it is temperature and humidity sensitive. A cooler environment will lead to the mattress feeling harder when you first lie on it. Usually even if a visco-elastic foam feels hard at room temperature, it will soften with the application of your body heat and mass, which means that your clothing and the showroom coverings may have also prevented to a certain extent the heat transfer and gave a false impressin of suportiveness. Foam softening would also be faster at home when the body heat becomes trapped under the bed coverings.
As memory foam softens in response to heat and humidity from your body or room temperature, it changes from a more elastic material into a more viscous material and the length of time it is continuously compressed can also affect how much the memory foam softens as well. This change or “melting” also takes time when you lie on it and it also takes time to change back to elasticity and return to its shape when you get up. These two factors are the main reasons that lead to the slower compression and recovery (the memory quality) of memory foam. For this reason, it would need a good support layer underneath it.
I know you are in a more complicated situation than you may have anticipated, but hopefully, you’ll make some good progress after some more experimenting. Keep us posted!
Phoenix