Hi zachneedmattress.
Thanks for your kind words, I am glad we can help.
The thickness of a mattress is just a side effect of the design and by itself isn’t particularly meaningful because whether a thicker or thinner mattress would be better or worse for any particular person will depend on the specifics of the materials (type, firmness, etc.) and on all the other layers in the mattress. Thickness is only one of many specs that are used to make different mattresses that perform and feel differently and that makes a mattress suitable for one person and not another. There is more about the effect of thickness in post #14 here. Regardless of how thick or thin a mattress may be … the most important part of the “value” of a mattress is how suitable it is “as a whole” for your particular body type, sleeping positions, and preferences in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). There is certainly no reason that at your weight you would “need” more thickness than either of the mattresses you are considering but you may still “prefer” a mattress that is thicker or thinner depending on the design.
A 170lbs, back sleeper should not need the extra thickness that a higher BMI would generally need to ensure a larger “range” of compression that a so that the mattress is not becoming too firm.
So the overall thickness of a mattress that is either “needed” or “preferred” would depend on the combinations of the layers and components that are needed to achieve the design goal of the mattress and provide the PPP (Pressure relief, Posture and alignment, and Personal preferences) that can best match each person and their unique body type, sleeping positions, and preferences.
Thinner latex mattresses are common in many parts of the world but only your personal testing can tell if this would be an appropriate thickness for you. A 7" mattress can be quite adequate for most adults, depending upon sleeping positions and body type and sensitivities.
The first thing to do is always to check with the mattress manufacturer you’re considering and ask their opinion to make sure that the foundation is appropriate and doesn’t void your warranty and you can check on this with Cozy Pure when you visit them.
There’s much more information about the functions of foundations, active slat systems and actual box springs in the foundation thread here. With most modern mattresses, the bottom piece of the mattress set is a foundation that does not flex. Closely spaced wood slats are quite common for the construction. This serves the purpose of allowing the mattress to be higher off of the floor for easier egress and ingress, and also to help promote better air circulation around the mattress.
A bed frame (or bed set) serves a similar purpose. It elevates the mattress set for easier access, and also promotes airflow around the complete mattress set.
I am glad that you managed to get some clarifications from Cozy Pure over the phone and that you are planning to visit them as nothing replaces personal experience. Their latex is Dunlop with a GOLS certification (only latex that gets this certification) and as they clearly state on web site it is 100% natural and not a blend. NR Dunlop would generally be more durable overall than a blend or synthetic (SBR) latex although there may be value in using a blend because it is less expensive and still a very durable material compared to other foams and in some cases a blend can improve the properties of the foam. FIY most Talalay produced worldwide is blended and usually Dunlop blends would have different percentages which vary with each foam manufacturer but I believe.
I look forward to hear about your decision and any insights you might have from your visit and testing of CozyPure’s products.
Phoenix