Hi CoraLee77.
Welcome to our Mattress Forum! 
There are no “standard” definitions or consensus of opinions for firmness ratings and different manufacturers can rate their mattresses very differently than others so a mattress that one manufacturer rates as being a specific firmness could be rated very differently by another manufacturer. Different people can also have very different perceptions of firmness and softness compared to others as well and a mattress that feels firm for one person can feel like “medium” for someone else or even “soft” for someone else (or vice versa) depending on their body type, sleeping style, physiology, their frame of reference based on what they are used to, and their individual sensitivity and perceptions. There are also different types of firmness and softness that different people may be sensitive to that can affect how they “rate” a mattress as well (see [url= https://forum.mattressunderground.com/t/ultimate-dreams-latex-versus-oklahoma-mattress-inner-spring-mattress-with-latex-topper]post #15 here[/url]) so different people can also have very different opinions on how two mattresses compare in terms of firmness and some people may rate one mattress as being firmer than another and someone else may rate them the other way around. This is all relative and very subjective and is as much an art as a science.
There are too many unknowns, variables, and personal preferences involved in choosing a mattress for someone else to make specific suggestions based on specs (either yours or a mattress) or theory at a distance that can possible be more accurate than your own careful and objective testing (using the testing guidelines in the tutorial post) which is always the most reliable way to predict which mattress will be the best match for you in terms of PPP (Posture and alignment, Pressure relief, and your Personal preferences) (see [url= https://forum.mattressunderground.com/t/ultimate-dream-mattress-firmness-level]post #2 here[/url]).
Hyperbole aside, this is more of a situation of you deciding what is “safe enough” for you.
“Toxic” is a term for poisonous substances produced within living cells or organisms, although the term is often used in the mattress industry (and often part of some “fear-mongering” campaigns), but I think I understand your point. Most people that are looking for “non-toxic” (toxicity is dose-dependent) mattresses or materials are usually concerned most with “safety”.
As there is quite a bit of confusing information available online about toxicity, safety and organic, 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, and more about some of the differences between organic and safety certifications in post #2 here and there are also 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, and what those certifications can mean to determine whether the contents of any particular mattress are “safe enough” for you.
I am sure that if you’ve done a great deal of reading on the site, you can clearly see that the focus on here is “how” to choose and that 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’m not sure what you’ve read since you found the site but just in case you haven’t read it yet … 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 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 (Posture and alignment, Pressure relief, and your own 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 (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.
Using a $800 upper limit budget in queen (mattress only), I took a quick look at the lists that are linked in the tutorial post and while I may have missed some … here are some quick results. All the links provided below are trusted members of this site which means that I think highly of them and they use good quality and durable materials and components within their mattresses.
Sedona Sleep sells a polyfoam base mattress
addable / sells a memory foam mattress.
SleepEZ also has this option which in Queen size would fit your budget.
Nest Bedding has their Love & Sleep Mattress .
Novosbed Canadian-only. Memory foam over polyfoam layer and polyfoam base.
Comfort Sleep Systems also has innerspring options that fit your budget.
[url= {admin note: discontinued product}]My Green Mattress[/url] with a few good options that fit your budget range.
Sleep EZ with their Natural Latex Mattress falls into your budget range as well.
Texas Mattress Makers with many good quality and low budget options.
Christeli has one memory foam option
There are also some lower budget latex and latex hybrid options that are listed in posts #3 and #4 here that are in “relatively” lower budget ranges (although some of these may be more than your budget).
Some of the new “simplified choice mattresses” that are also in relatively low budget ranges (from $600 to $1000 queen size) are also listed in post #2 of this topic and may also be worth considering as well although most of them are also more than your budget range.
I hope this helps. Once you have a chance to narrow down your finalists please let me know and if you have more specific questions I’ll be happy to assist you.
Phoenix