Hi Odontoid,
My reply to a similar question in post #2 here would be the same as I would reply to your questions as well.
The shorter answer is that I would avoid all the major brands such as Simmons, Sealy, and Serta completely whether they are supposedly “on sale” or otherwise (see the guidelines here) because you won’t be able to find out all the information you need to make an informed choice about the quality and durability of the materials in the mattress or make meaningful comparisons to other mattresses and the upper layers of the mattress would include lower quality/density materials that would be a significant weak link in the mattress in terms of the durability and useful life of the mattress.
In addition to that the only way to know whether another mattress will feel similar to you will be based on your own personal experience and comparisons because there wouldn’t be another manufacturer that makes a mattress that is specifically designed to “match” the Beautyrest World Class Resonance.
As you discovered … most people that have spent more than a couple of hours on this site would know more meaningful information about mattresses and mattress materials than most of the salespeople in the mainstream industry that sell them and I personally wouldn’t spend any time in chains stores such as Mattress Firm even if you are only testing mattresses because most of the time you spend there will be wasted if you aren’t able to find out the specifics about what is inside the mattresses you are testing.
The information you will need to ask meaningful questions are in the other reply I linked but I would take your time and follow all the steps in the tutorial one at a time. With an “appointment” retailer I would especially make sure that you can find out all the information you need to make an informed choice and I would make sure that you don’t get “tempted” by any special “deals” they offer you in an effort to create a sense of urgency for you to buy one of their mattresses before you are ready to make your purchase or have made some meaningful comparisons with other stores and mattresses. Keep in mind that good quality/value mattresses are available every day of the year.
If you let me know your city or zip code I’d also be happy to let you know about any of the better options or possibilities I’m aware of in your area.
Phoenix