Hi rapscalli0n,
As you mention … these are not mattresses but component parts that you put together yourself at home and they have not passed the 1632 or 1633 fire code.
As far as a fire barrier goes … some people may consider a fire barrier to be important and some would be very happy not to have it and avoid the the chemicals that some of them contain (although some fire barriers such as wool that are used in more “natural” mattresses to pass the test this would not be a concern). The actual materials they are selling use the same latex as many other manufacturers yes. You can read more about fire barriers and the complex and controversial issues surrounding mattress “safety” and chemicals in a mattress in post #2 here. People who are sensitive to the chemicals used in some fire barriers can also get a prescription for a chemical free mattress which allows a manufacturer to sell a mattress without a fire barrier.
I know the blended Talalay contains filler (a form of silicate material is used) but I’ve never asked them about their 100% natural formulation although I would imagine it contains them as well. Fillers can shorten the life of a foam or reduce its cost or they can add various desirable properties to the foam including durability as well. It’s never as simple as just “fillers are bad” and it all depends on the specific formulation and chemistry of the foam and the type and amount of fillers used. There is more about the different types of latex in this article and post #6 here
I usually don’t buy into any “best worst” arguments. Everything usually has a tradeoff of some kind and what is “best” is up to each person to decide based on their preferences. 3 layer mattresses have the advantage of being able to re-arrange or exchange more layers to adjust the feel and performance of the mattress in more ways than a 2 layer mattress. Even a 1 layer mattress that matches someone’s needs and preferences would be fine for the person that prefers it and in that case there would be no reason for more. Sometimes simpler or less complex can be easier to predict in terms of changes and there can also be cost advantages to layers that don’t need to be cut from the original 6" core.
There is nothing intrinsically “wrong” with putting softer latex under firmer latex to a point. I would tend to avoid thick layers of any soft material on the bottom of a mattress (although thinner layers such as those in a two sided mattress are usually fine as well) because it could affect alignment and support but other than that the sky is the limit and each person can decide for themselves which type of layering they prefer or best matches their needs and preferences.
A firmer layer over a softer layer in certain types of mattress designs is called a “dominant layer” and some people even prefer its feel and performance although it’s typically done with relatively thinner layers of firmer foam over thicker layers of softer foam or in quilting layers. If 6" of latex matches your needs and preferences then there is nothing wrong with that either although thinner mattresses will tend to be firmer than thicker mattresses with the same layers on top of it and may not be as adaptable to different body types and sleeping positions as thicker layering. At your weight you certainly wouldn’t bottom out on 6" of latex but only you can decide if it matches your needs and preferences in terms of PPP (Pressure relief, Posture and alignment, and Personal preferences).
Again … I would avoid the type of thinking or assessment that thinks in terms of “better or worse” and find out where in the range you may be with any choice you have. The best way to answer these types of questions is to talk with them so they can explain the advantages and disadvantages of the different options they offer and then make a choice based on the benefits and tradeoffs that are most important to you. The more wool you have on top of the latex the more it will affect the feel of the latex and its ability to compress and take your shape under your weight and the more you would feel the properties of the wool. Wool is also very good at controlling temperature and humidity in a mattress. Some people even have a thick wool topper on top of their mattress because they love the feel of sleeping on thicker layers of wool and others have as little wool as possible or no wool at all so that they can feel more of the latex comfort layers. All of this is personal preference.
Your questions and uncertainty also reinforces the argument mentioned in the two or 3 latex layer question that sometimes less options are “better” because they can help alleviate uncertainty and make choices easier
Some covers are washable and some aren’t. Again these are questions that should go to the retailer or manufacturer themselves so they can give you the answers that apply to the materials and components they sell.
Nothing stops it. In general manufacturers and wholesalers don’t sell to the public in small quantities but many people buy component parts to make their own DIY mattresses. You can see some examples of where you can buy these in post #4 here. If you go in this direction and decide to work outside the guidance of a mattress manufacturer, most people will find that mattress layering and design and the selection of components can be more complex and takes more skill and knowledge than they were prepared for and often end up spending more than they would have if they had worked with a mattress manufacturer who sells mattresses with exchangeable layering that could have helped them avoid all the mistakes they made.
Phoenix