Hi dcain,
Welcome to the Mattress Forum! 
This site itself isn’t a review site, but Sleep On Latex is a member 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 do offer products using high quality componentry.
Regarding “reviews” themselves, while other people’s comments about the knowledge and service of a particular business can certainly be very helpful, 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 (Posture and alignment, Pressure relief, and your Personal preferences) 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’m sorry to hear about your back issues. 
Because each person is different in terms of their physiology, weight distribution, and body shape as well as the positions they sleep in, their individual preferences, and the specifics of any back issues they may experience, there unfortunately is no such thing as a mattress that is “better for backs” in general because a mattress that is good for one person’s back (or back issues) may be completely unsuitable for someone else to sleep on … even if their body type, sleeping positions, or back issues appear to be fairly similar. There is only a mattress that keeps you in good alignment which would be best for YOUR back.
In general, what you would be looking for is a mattress with firm enough deep support and then comfort layers that are “just enough” in terms of thickness and softness to “fill in” and support the more recessed parts of your sleeping profile and relieve pressure in your most pressure prone sleeping position (usually side sleeping for those who sleep in this position) so that there is less risk to alignment in your other sleeping positions.
There is a lot of misleading information in the industry about fire retardants and “chemicals” ranging from significant “fear mongering” on one side to completely minimizing fire retardants as an issue at all on the other. Like most issues that arouse strong feelings or controversy the most reliable and “accurate” information tends to be in between both polar extremes so there is “some truth” that “some mattresses” may use some chemicals that some people would find questionable or wish to avoid.
There is also more about “safe” fire barriers in this article and post #2 here. 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 are other brands who will use a wool layer as a method to pass fire retardant guidelines (such as Sleep on Latex).
This is a common complaint of many mattress shoppers, as too many offerings use lower density and lower quality materials that tend to provide a very short comfort life. When shopping for a mattress, 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 case you haven’t read it yet … the best place to start your mattress buying 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 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”, 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).
With this information you’ll hopefully be on your way to making an informed mattress buying decision.
Phoenix