Hi jinga,
Welcome to the Mattress Forum! 
You have quite a few questions that go in a multitude of directions. Instead of answering all of them, which will be counterproductive, I’ll focus on a few key themes that I believe will be most helpful to you.
The first deals with how to shop for a mattress.
While I can certainly help with “how” to choose, it’s not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best “match” for you in terms of “comfort”, firmness, or PPP (Posture and alignment, Pressure relief, and your own Personal preferences) or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or “theory at a distance” that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
I know you did some learning about mattresses 10 years ago, but I would suggest you start again by reading the mattress shopping tutorial here. 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”, firmness, and PPP 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 (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
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 the 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.
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.
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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.
Addressing some of your “health concerns”, mattress are not required to use flame retardant chemicals. They are simply required to pass 16 CFR 1632 and 1633. The most common method used to pass the regulations in the mattress industry is the use of inherent, “non chemical” fire barrier fabrics that are either quilted into the cover or are wrapped around the inner materials of the mattress like a sock and foams that use fire retardant chemicals are much more common in the furniture industry than they are in the mattress industry. There is also more about “safe” fire barriers in this article and post #2 here and the posts it links to at the end.
Most people that are looking for a “healthy” mattress are usually concerned more with “safety” than whether the materials have an actual organic certification (all new mattresses will off gas something). There is more information about the three different levels of organic certifications in post #2 here and some of the benefits of an organic certification in post #3 here and there is more about the different types of organic and safety certifications in post #2 here and more about some of the differences between organic and safety certifications in post #2 here and there are some comments in post #42 here that can help you decide whether an organic certification is important to you for environmental, social, or personal reasons or whether a “safety” certification is enough.
While it may be more information than you are looking for … there is also a lot more information in post #2 here and the more detailed posts and information it links to about safe, natural, organic, “chemical free”, and “green” mattresses and mattress materials that can help you sort through some of the marketing information and terminology that you will encounter in the industry and can help you differentiate between them and answer “how safe is safe enough for me” or “how natural is natural enough for me” and that can help you decide on the type of materials and components you are most comfortable having in your mattress or on the certifications that may be important to you. These types of issues are complex and are generally specific to each person and their individual sensitivities, circumstances, criteria, beliefs, and lifestyle choices.
I wouldn’t be too concerned with reviews, as they are generally the least reliable manner to choose a mattress, and I instead recommend focusing upon componentry as outlined in the mattress shopping tutorial that I linked to earlier. While other people’s comments about the knowledge and service of a particular business can certainly be very helpful, I would always keep in mind that you are the only one that can feel what you feel on a mattress and I would be cautious about using anyone else’s suggestions, experiences or reviews on a specific 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. 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 in terms of comfort, firmness, and PPP may be completely unsuitable for someone else to sleep on (even if they are in a similar weight range). In other words … reviews or other people’s experiences in general won’t tell you much if anything about the suitability, quality, durability, or “value” of a mattress for any particular person (see post #13 here).
I would avoid rushing into making a decision but instead take your time and read through the information I’ve provided, as it will offer you the best possible chance of making an educated and quality choice. And I would pay too much attention to the special “sales events” this weekend. Better retailers don’t have large “fake sales” based upon holiday events holidays (see the guidelines here and post #5 here), but they may occasionally have smaller discounts for special events or promotions.
I’ll be happy to assist with any questions you may have once you’ve read through the information here and if you have questions about anything you may have seen locally. If you do end up wishing to shop online, you may wish to consider the members here of this site which means that I think very highly of them and that I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency. They are extremely knowledgeable about latex, memory foam and different innerspring configurations, and I would not hesitate to recommend them for your consideration.
Phoenix