I’ve been doing a ton of research on mattresses over the past month. So many black boxes.
anyway:
In a latex mattress that consists of multiple layers such as the sleep ez which is 4 x 3" layers, to the extent that there is sagging/indentations that occurs is that generally confined to to top most layer? In other words down the road if we experience sagging is it possible to just replace the top layers or does that reflect problems throughout the various layers?
Also does susceptibility to sagging/indentations vary across types of latex Dunlop vs talalay 100% or natural vs blended?
If the cause of the sagging is in the mattress rather than the support system underneath it then in almost all cases yes you can just replace the top layer instead of replacing the entire mattress. The primary cause of foam softening and virtual or visible impressions are the continuous and ongoing deflection and compression of the materials inside it and since softer top layers will be subject to more compression and deflection more than the deeper firmer layers they will tend to soften and break down before the others and in most cases the deeper layers will still be fine if the softer top layers need replacing.
All latex is a very durable material relative to other types of foam materials and in practical terms they would be closely comparable in terms of durability (with the possible exception of 100% natural Talalay in softer ILD ranges) so I would treat the different types of latex as a preference and budget choice rather than a better/worse choice. There is more about the different types and blends of latex in post #6 here and there is more about the more general differences between Dunlop and Talalay in post #7 here.