Hi sleepyvet,
You can red more about some of the benefits of a thicker mattress in post #14 here. With your greater weight… you may find that a thinner mattress (such as the 7000) may not have the range to adapt as comfortably to all your sleeping positions and may be firmer than you prefer (as it would be closer to its maximum compression). I would suggest that 8 - 9" of latex would be better and you are in the weight range that 12" of latex may also benefit you (especially if you sleep in multiple positions).
In terms of durability … the thinner mattress would compress more to a greater percentage of its thickness and this would be less durable yes. Durability is also affected by the firmness of the layers with firmer foam being more durable than softer foam. With a thicker mattress … the top layer may be less durable than the others but this can be easily replaced and the others can be kept.
This would depend on the various durability factors which includes the type of latex, the softness of the layers, and any other materials in the mattress but if all else was equal … then a two sided mattress will be more durable than the same layers in a single sided mattress yes … even with latex. It won’t be “twice as much” because all the layers compress in use whether they are on the top or bottom of the mattress but it would make a significant difference IMO. There are always tradeoffs involved though because a two sided mattress has some design tradeoffs because it can’t use thicker softer layers in the comfort layers to the same degree because when they are on the bottom it could affect alignment (it would have the softer layer on one side for comfort and also on the other side which would be part of the support and this can result in higher amounts of softer latex in the mattress).
A platform bed performs exactly the same function as a foundation so from the perspective of support it would be identical as long as both the platform bed and the foundation had the same type of support surface and were equally well supported to the floor. The platform would need center legs and midbeam or center support to the floor.
Just like with a foundation … my preference would be to have a slatted non flexing surface with no more than 3" in between the slats (preferably less) with an all latex mattress because this allows for greater ventilation of the mattress.
The biggest reason that a foundation may be needed on a platform bed (that had a suitable surface) would be to add height … not for any extra support.
Feel free to post your questions whenever the come up :0
Phoenix