Hi insearchofsweetdreams,
Just in case you haven’t read it yet … the best place to start your mattress research is the tutorial post here which has all the basic information, steps, and guidelines that you will need to make the best possible choice … and know how and why to avoid the worst ones.
Post #13 here has more information about the most important parts of the value of a mattress purchase.
As you can see … the most important part or “value” is how well a mattress matches your specific needs and preferences in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) and the best way to tell this is by careful and objective testing on a mattress using the testing guidelines in the tutorial post. If it’s not possible to test a mattress in person before a purchase then a more detailed conversation with a knowledgeable and experienced online retailer or manufacturer who is more interested in selling you the “right” mattress for your body type and sleeping positions than they are in selling you anything you will buy is the next best way to decide whether a mattress would be a good match for you (see mattress firmness/comfort levels in post #2 here).
It’s not possible for a manufacturer to “rate” a mattress in terms of pressure relief or spinal alignment because they would both be different and relative to different people and a mattress that provides good alignment or pressure relief for one person may be completely unsuitable for someone else to sleep on depending on their body type, sleeping positions, and individual sensitivities and preferences. Even firmness ratings aren’t consistent between different manufacturers or even between different people and a mattress that feels “too firm” for one person or even a group of people can feel “too soft” for someone else. All mattresses provide some degree of pressure relief (at least compared to sleeping on a hard surface with no give at all) but only your own personal testing or experience can tell you whether a mattress is a good “match” for you and provides you with good alignment and good pressure relief in all your sleeping positions.
After PPP … the next most important part of the value of a mattress purchase is to make sure you know the quality of all the materials in a mattress (see this article) so you can compare them to the guidelines here to make sure there are no “weak links” in the mattress and make more meaningful comparisons with other mattresses. Without this information you would be making a “blind purchase” which is very high risk and has a high chance of buyers remorse much too quickly. If you can find out the specifics of all the layers in the mattress then I’d be happy to make some comments about the quality and durability of the materials inside it.
In other words it boils down to testing for suitability, checking specs for durability, and then comparing each mattress with your other finalists based on all the parts of your personal value equation that are most important to you (including the price of course and any return or exchange policies if that’s also an important part of your purchase decision).
You can see my comments about the Gemma mattress in post #2 here and the memory foam is on the low side (3.2 lbs) in terms of density but I would always confirm the quality/density of all the layers in a mattress before you purchase it not just a single layer.
While the Gemma deserves credit because it’s one of the few memory foams that are Oeko-Tex certified for VOC’s and harmful substances … I would also be aware that all latex mattresses are also Oeko-Tex or Eco Institut certified to the same standards and they are a more resilient material than memory foam if you prefer to sleep “on” your mattress. There is more about latex vs memory foam in post #2 here.
Phoenix