Hi mikkel,
I think there may be two separate issues involved here. One is the amount of latex vs polyfoam in a mattress and the second is when it may be either a good idea or a preference to use more than about 8" or 9’ of latex in a mattress.
Speaking generically you can see my thoughts about an all latex mattress vs a latex hybrid in post #2 here. Brooklyn Bedding also has an all latex mattress on amazon which is not yet on their main site. I think though that the SleepEz 10000 would be closer to an “apples to apples” comparison with both of them (although of course the Alexis would be lower cost than both because it only has 6" of latex and the other two have 9")
On the other hand you can see some of my thoughts about a latex mattress that uses more than about 8" - 9" of latex and when this may be useful or a preference in post #14 here.
The Alexis is “in between” an all latex mattress and a typical latex/polyfoam hybrid which only has a latex comfort layer and I would certainly choose a mattress with a latex middle transition layer over one that had only latex on top (particularly for heavier people that may compress the layers below the top latex layer more) but I would also choose all latex over either if I could comfortably afford it. It’s really a matter of the tradeoff between budget and performance and the deeper the polyfoam layer is the less effect it will have overall on both performance and durability.
For most people though (unless they were very heavy) … 12" of latex would be more than they really “needed” although it may still be a good choice either as a preference or because a mattress they were buying needed more thickness to accomplish its design or performance goals.
Phoenix