Hi tiredben,
It’s good to see that you did some good testing 
I would suggest narrowing down your choices among the PLB line to the “best” one for you in terms of PPP (Pressure relief, Posture and alignment, and Personal preferences) and use that and the “best” layering of the Savvy Rest as your guideline. You have quite a “range” of mattresses that you like and they are all very different so they would not be a very useful guideline because they are not specific enough to your needs and preferences.
I would also tend to avoid latex in ILD ranges as soft as 15 because they would be much more risky for you both in terms of alignment and in terms of durability (and I think most manufacturers would suggest this as well). Heavier weights tend to need and do best with firmer latex than lighter weights would.
As you probably know … Arizona Premium is a member here and like all the members here I believe they are among the best quality and value in the country. They are much more familiar with their own mattress designs and the options they provide than I am so I leave the comfort and design choices to your more detailed conversations with them which is much more effective than any “theory at a distance” I could offer.
They also told me yesterday that they have a new coupon code for the member discount they give to the forum members and I haven’t updated the site yet but in case you need it the code is MU5 although just telling them on the phone is usually enough which is the way the discount works for most of the members here.
The other members of the site that sell online (several of whom also have latex mattresses with various versions of exchangeable layering) are listed in post #21 here.
Phoenix