Hi alha02.
Welcome to our Mattress Forum. 
We are glad you’ve found our resources useful and can see you’ve got a list of great vs great options to choose from!
With regards to the Nest Hybrid Latex…
At your BMI, if there is a lower density layer that is deeper in the mattress and has an inch or two of higher quality and more durable materials above it, even if it is slightly lower than our minimum guideline of 1.5 lb per cubic foot density for polyfoam, it may be considered a reasonable compromise/decision where durability is concerned. I wouldn’t be especially concerned in this particular case. Also, the cover is removable and (to my knowledge) replaceable, also eliminating it as too big a factor as a weak link.
For the QuadraFlex and Ultimate Hybrid…
There is a great topic about zoned coils by Phoenix that may address your zoning concerns. And to take a few more words from Phoenix…
Zoning systems of various types can sometimes be useful and worth considering for people that have more difficulty finding a mattress with the right “balance” between comfort/pressure relief (under the shoulders especially) and support/alignment (under the hips/pelvis especially) or who have more challenging circumstances or sensitivities, body types that are more difficult to “match” to a mattress, more complex medical issues, or who have a history of having more difficulty in finding a mattress that works well for them. There is more about zoning in this article and in post #11 here and the additional posts it links to but once again the only way to know whether any specific mattress (zoned or otherwise) will be a good “match” for you in terms of PPP will be based on your own careful testing and/or your own personal experience.
With zoning, you’d need to take into account how your weight is distributed the distance between the hip and shoulders and where within the mattress you need to position yourself to get the desired alignment and comfort and to add to this you’d need to consider how your choice will be appropriate for your fiancée. Of course, that can be solved with the split king but you have many more variables to work with when dealing with zoning and you may be facing the classic dilemma of a couple with different needs and preferences that need to be designed into the same mattress or “sleeping system”.
I am sure you came across this article already but it is worth reading about innersprings and their differences here it in the context of zoning.
And for SleepEZ…
It’s hard to say for sure what your experience would be here. Side sleepers can get away with 2" in the comfort layer, and you’ll know if that’s not adequate enough because you’ll begin to experience pressure points during the course of the night and could have symptoms of numbness, soreness, localized redness, or end up tossing and turning all night as your body tries to relieve the pressure (when side sleeping). But, if you’re primarily back/stomach sleepers, I thin the 2" would be unlikely to be problematic for you.
I hope I’ve been able to help you as you make your decision! Please do feel free to ask any other questions that may arise.
NikkiTMU