Hi winterDreamer,
Welcome to the Mattress Forum! 
You’re a bit all over the map here, so the best advice I can offer you is to “reset” how you’re going about shopping for a mattress.
The first thing I would start with is the process of shopping for a mattress, and then I’ll address a few of your other statements.
The first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly help you know how and why to avoid the worst ones.
Two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort” and PPP (Posture and alignment, Pressure relief, and Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists (based on all the parts of your personal value equation that are most important to you).
In its simplest form … choosing the “best possible” mattress for any particular person really comes down to FIRST finding a few knowledgeable and transparent retailers and/or manufacturers (either locally or online) that sell the types of mattresses that you are most interested in that are in a budget range you are comfortable with and that you have confirmed will provide you with the all the information you need about the materials and components inside the mattresses they sell so you will be able to make informed choices and meaningful comparisons between mattresses and then …
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Careful testing (hopefully using the testing guidelines in the tutorial) to make sure that a mattress is a good match for you in terms of “comfort”, firmness, and PPP … and/or that you are comfortable with the options you have available to return, exchange, or “fine tune” the mattress and any costs involved if you can’t test a mattress in person or aren’t confident that your mattress is a suitable choice.
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Checking to make sure that there are no lower quality materials or weak links in a mattress you are considering relative to your weight/BMI range that could compromise the durability and useful life of the mattress (see the durability guidelines here).
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Comparing your finalists for “value” based on #1 and #2 and all the other parts of your personal value equation that are most important to you.
The only reliable way to assess the “safety” of different materials in more general terms is based on lab tests and the certifications they have for harmful substances and VOCs (regardless of whether they are organic or natural or synthetic) so that you have some assurance than the VOCs are below the testing limits for the certification. If the materials in a mattress or the mattress itself has a reliable “safety” certification, then for most people they would certainly be “safe enough” … regardless of the type of material or the name of the manufacturer on the label. There is more about the different types of organic and safety certifications such as Oeko-tex, Eco-Institut, Greenguard Gold, C2C, and CertiPUR-US in post #2 here.
While again nobody can speak to how any specific mattress will “feel” for someone else or whether it will be a good “match” in terms of comfort, firmness, and PPP because this is too subjective and relative to different body types, sleeping positions, and individual preferences, sensitivities, and circumstances and you are the only one that can feel what you feel on a mattress … outside of PPP (which is the most important part of “value”), the next most important part of the value of a mattress purchase is durability which is all about how long you will sleep well on a mattress. This is the part of your research that you can’t see or “feel” and assessing the durability and useful life of a mattress depends on knowing the specifics of its construction and the type and quality of the materials inside it regardless of the name of the manufacturer on the label or how a mattress feels in a showroom or when it is relatively new so I would always make sure that you find out information listed here so you can compare the quality of the materials and components to the durability guidelines here to make sure there are no lower quality materials or weak links in a mattress that would be a cause for concern relative to the durability and useful life of a mattress before making any purchase.
You’ll always want something that has a good support unit. When sleeping prone, you’ll want to make sure that the bed doesn’t “bend in” too much and accentuate the lordotic curve of your low back. When sleeping on your side, you’ll want to make sure that the mattress provides “enough” comfort to allow your shoulder and hips to sink in while maintaining a more neutral alignment. As you go from one extreme to the other, you’ll want to find a product that, for you, offers a bit of each.
While other people’s comments about the knowledge, service, and guidance of a particular business can certainly be helpful … I would generally avoid using other people’s experiences or reviews on a mattress (either positive or negative) or review sites in general as a reliable source of information or guidance about how you will feel on the same mattress or how suitable or how durable a mattress may be for you and in many if not most cases they can be more misleading than helpful because a mattress that would be a perfect choice for one person or even a larger group of people may be completely unsuitable for someone else to sleep on (see post #13 here). The fact is that the only thing a mattress review will usually tell you is how one person likes a particular mattress which is usually based only on initial or early impressions that are very subjective and little else. Using reviews is the least desirable and least accurate way to select a mattress.
My Green Mattress is a member here, which means that I think highly of them. Their mattresses come from Tim’s factory in LaGrange, IL. MyGreenMattres.com is their online business. Their mattresses would be quite different from the Tuft and Needle – latex and latex/coil versus polyfoam.
When you can’t test a mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer like My Green Mattress that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the properties and “feel” of the materials they are using and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked or other mattresses you are considering that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs, options, and firmness levels to different body types, sleeping positions, and preferences (or to other mattresses that they are familiar with) than anyone else. Post #2 here and this topic have more about the pros and cons of a local vs an online purchase.
If you’re considering something local (besides Sears), you can provide your zip code and I can see if I am aware of any better retailers close to where you live.
Phoenix