Hi PandaRage,
Leisure Industries hasn’t been mentioned a lot in the forum but they are a good choice IMO and they are certainly among the best value in the area. This thread has more feedback about them (which I suspect is the one you’ve seen).
With you sleep in a mix of sleeping positions that includes stomach sleeping then “just enough” in terms of thickness and softness to relieve pressure in your most pressure prone position (usually side sleeping) is always best for alignment when you are sleeping on your stomach because stomach sleeping has a significant risk of sleeping in a swayback position where your pelvis sinks down too far and can cause alignment issues and lower back discomfort and pain. I would always choose comfort layers that were slightly thinner and firmer over thicker and softer in this case all other things being equal.
No this would not be a concern for me at all. The bottom layers of the mattress are not nearly as subject to durability issues as the upper layers and a bottom layer of very firm foam of this density can help even out the support surface of the mattress on a foundation and protect the foams above it from sinking in to any gaps and provides more even support for the layers above it as well. It can also act as a “stabilization” layer in preventing side to side sway and can also help with the handling of the mattress when it is being constructed. This same type of layer is often used under an innerspring to provide it with some shock absorption and even out the surface the springs rest on. It doesn’t need to be the same density as the higher density and higher performance foams above it and using these would tend to add more cost than value … it just needs to be firm and durable enough for the application.
No … quite the opposite as a matter of fact. I’ve mentioned on quite a number of occasions that a mix of a thinner layer of memory foam and a thinner layer of latex is one of my favorite comfort combinations (with either one on top depending on preference) and has a rather unique feel which is a combination of the resilience of the latex and the slower and soft feel of the memory foam. It is also a much less “risky” combination than thicker layers of memory foam where you sink in more deeply and is more “movement friendly” than thicker layers of memory foam as well. You can see a little more discussion about this type of layering (thinner layers of memory foam over more resilient layers underneath them) in this post about the Tempurpedic weightless line and in this post about this type of layering in general.
Based on all of this as well … if everything else seemed roughly equal and pressure relief was good in all your sleeping positions I would tend towards the slightly thinner comfort layer which would put you a little closer to the latex and could be a little less risky.
Phoenix