Hi Yogimama,
I think the post you are mentioning which replied to sleepyvet has most of the relevant information about the structural differences between them but there may be more involved as well.
For heavier weights … a thicker mattress can be more suitable because it allows for a smoother transition from soft to firm with changing positions, can accommodate different layering and designs that can meet the needs of different sleeping positions more effectively, and won’t get firm as suddenly as thinner mattresses or layers. There is more about this in post #14 here. There is also more about the many factors that are involved in the durability of a mattress in post #2 here.
Overall though … if you sleep on your back or stomach (the two “flatter” sleeping positions" that are less pressure prone) you could probably “get away” with 6" of latex even with your heavier weights although some extra softness on top may still be preferable especially for back sleeping. If you sleep on your sides then you will likely need a comfort layer of softer foam to accommodate your pressure points because 6" of latex that was suitable for support on your back or stomach may not provide the degree of pressure relief that many people would prefer on their sides. You are not in the weight range that would need more than 8" - 9" of latex but I would suggest that in most cases you would probably do better with something thicker than 6" although your own personal testing would help you know for sure.
When you are looking at the choice between a polyfoam/latex hybrid … then of course budget would be a primary consideration because not everyone can afford an all latex mattress no matter how much they may want one and I have even seen people that don’t seem to be able to tell the difference between a polyfoam, innerspring, or latex support core (although that’s hard for me to imagine). There is no point in paying for something that provides no meaningful benefit for someone although feeling a difference may not always be the whole picture because it may also be about the discomfort or other “symptoms” that they don’t feel but don’t know is connected to a mattress they sleep on.
Polyfoam in the density range of 2.35 lbs is a very durable material … although not as durable as latex in the firmness levels that would be used in support layers … so neither one has an obvious weak link in terms of durability. beyond this though the main difference would be in its performance and ability to adapt to all your sleeping needs and preferences (in a way this is similar to the benefits of a thicker mattress).
I don’t think there’s any doubt that with your weight an all latex mattress would last longer (and “lasting” here means remaining closer to its original specifications for longer rather than materials completely wearing out) and perform better but again this can vary depending on each person’s experience on a mattress. The most common reason that people need to replace a mattress is not so much that the materials have completely worn out or “collapsed” but that the gradual loss of comfort and support that happens as all materials soften or change over time has crossed a threshhold where it no longer meets their needs and preferences and they gradually become uncomfortable or experience the onset of various symptoms. Latex stays closer to its original specifications for a much longer period of time than polyfoam and for many people who can comfortably afford it this means better value and better sleep even though the initial cost is higher.
Phoenix