Hi LJsleep.
I thought I answered your post but now I see that you actually posted twice very closely. I’ll do my best to answer your questions.
It looks like you need a hard reset with your research and start with reading through the tutorial post 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 which would include the major brands such as Serta or any mattress where you aren’t able to find out the quality of the materials inside it. The “sagging” you are experiencing is most likely a compression/breakdown of the quilt panel and comfort layer foam due to lower quality density memory foams and/or polyfoams.
I don’t have enough information about your body type, sleeping positions or more specific descriptions of your symptoms or what parts of your body you are experiencing to make any meaningful comments but the first step is always to determine whether your “symptoms” are from pressure issues, alignment issues, or “feel” issues … all of which could have different solutions.
To learn “to tell” the difference about pressure relief and support, you can read about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel”. “Support” is often misunderstood because the goal of a “supportive” mattress is to keep the spine and joints in good alignment and this requires the type of contouring support that allows some parts of the body to sink in more and some parts of the body to sink in less and this will vary on an individual basis. Also some of the forum posts that talk about fine-tuning a mattress and may help you recognize or “diagnose” the underlying cause of different types of “symptoms”, pain, or discomfort that may be connected to a mattress include …
Post #2 (this is the primary reference post for different “symptoms” that people may experience when they sleep on a mattress)
Post #45 (this is particularly worth reading as well)
You may also wish to read Post #3 here which will walk you through how to track down the cause of the back pains you and your mom are experiencing.
One of the ways people assess their body’s posture on the mattress is to take a picture of themselves lying on the mattress surface. Most pictures of this type show the person lying on his/her side. It is not very accurate but if taken at 90 degrees from the edge and as flush with the surface as possible it may reveal the alignment issues and give you a good indication of what is going on. While side sleeping may not be your primary sleeping position, it may shed some insight into your body’s angle as it interacts with the mattress. Given the needs you describe (durability, edge support, top layer comfort over deep support), you would probably do well with an innerspring / pocket coil hybrid mattress design.
Short of doing research and learning a bit about mattresses the next best option is to find a manufacturer or outlet that provides accurate information about their mattresses and the materials in it and is also skilled at fitting" their mattresses to your needs and preferences. Once you have done this … then choosing a mattress with their knowledge and guidance that fits your height, weight, body shape, sleeping positions, and preferences is much simpler. Of course the more testing you have done locally on mattresses that have a known construction… the easier it is to use your testing as a prototype for the type of mattress that would work best for you.
Latex allergies have been extensively discussed on TMU and a quick search (just click here) would bring up many posts. Allergy to Latex may be a confusing subject and complex to diagnose, in fact, many people that have other sensitivities attribute it to latex allergies. I would check what type of allergy you have because even though you might have a sensitivity to unprocessed rubber such as the one found in latex gloves….the latex used in a mattress is vulcanized and this process reduces the number of allergens in the rubber so that even some people with latex allergies would not have a sensitivity to a latex mattress. Without getting too technical the antigen proteins are responsible for creating an allergic reaction and when the rubber is heated to a much higher temperature to form the latex foam the antigen structure in the protein changes.
I know that this is quite a bit of reading but unfortunately there is no shortcut to it to make sure that you find a suitable mattress for you and your mom.
Phoenix