Hi Raksha14,
The first place I would start is to spend an hour or two reading the mattress shopping tutorial here which has all the basic information, steps, and guidelines you will need to make the best possible choices … and know how and why to avoid the worst ones … including any of the major brands (such as Simmons) or any mattress where you can’t confirm that they use good quality materials inside the mattress.
Gardner would certainly be a much better place to shop because they make good quality/value mattresses that use much better quality materials compared to the mainstream choices you are considering. Assuming you are in the Boston region … once you get to step 3 in the tutorial then the better options or possibilities I’m aware of in your area are listed in post #2 here. You have some good options available to you.
While a picture would help … it certainly sounds like your bedframe need some reinforcement to be able to hold a foundation, a mattress, and you and it would almost certainly void a warranty and probably damage your mattress. A bedframe should have at least 5 cross wooden cross slats or 3 steel cross slats with good center support to the floor to be able to support a suitable foundation and the mattress. Post #5 here has some links to the type of cross slats that I would suggest. You could also have it custom reinforced with enough wooden slats to support the mattress directly without a bunkie board or foundation (again making sure you have good center support to the floor)
If you are restricted in terms of height then it may be worth considering either a low profile foundation (generally about 5" or so) or a bunkie board (see post #4 here and the post it links to) under your mattress.
You can read more about the many variables that can affect the sleeping temperature of a mattress in post #2 here but in general terms if you are only comparing different types of foams used in comfort layers then latex would be the most breathable and temperature regulating followed by polyfoam followed by memory foam which is generally the warmest. While almost all mattresses use some type of foam in the comfort layers … some mattresses use natural fibers instead of foam and they would be the coolest of all … but are generally much more costly.
This is answered in the tutorial post and the links it includes (including this one) but the short answer is I would avoid both of them completely (and the other major brands as well).
No. I would suggest using the testing guidelines in the tutorial post.
Most new mattresses will go through an initial break in period yes where the foams lose any of their “false firmness”, the cover stretches and becomes less stiff, and any fibers settle and compress a bit so they will generally feel firmer for the first few weeks. I would try to choose a mattress that doesn’t need a topper and is already a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) unless you can test the specific mattress/topper combination in the store. If in spite of “best efforts” you end up choosing a mattress that is too firm and can’t be adjusted or exchanged and needs a topper … then a topper that is “just enough” to relieve your pressure points in terms of thickness and softness and no more will be less risky in terms of support/alignment. Post #2 here and the posts it links to includes the topper guidelines I would suggest if you need to choose a topper but I would cross that bridge only when and if you need to.
It would depend on the knowledge and experience of the particular salesperson and/or on the specifics of what they are telling/selling you (there would be no way for me to know specifically because I wasn’t there) but in most cases I wouldn’t walk through the front door of most chain stores to even have to decide whether what you are being told can be relied on because they don’t sell anything that I would consider buying anyway.
Phoenix