Hi jchiu003,
I can see that you share similar preferences to me… and these are the same choices I would make on a personal preference level.
The only challenge of this step is that at Macy’s they can’t generally tell you what is in their mattresses but at this stage you are only looking for the overall “feel” so they can certainly be part of your “playground” 
This would put you in the “average” range of what would work well for most people.
This also seems to be in a reasonable range.
I don’t know the details of their innerspring but in terms of material cost generally latex will be more costly unless the spring is a much more premium version than you would usually find.
While neither would be the “weak link” of a mattress and would probably outlast the comfort materials … as a material latex would generally be more durable.
Flexus buys their latex from the same sources as other manufacturers and it would depend on the type of latex they used in the mattress. Post #2 here talks about the inherent anti-fungal nature of natural latex and why latex is also more resistant to dust mites. I have seen no evidence that latex is anti-bacterial and while I see this claim a lot … I have seen nothing to support it and it also seems to go against the evidence because when liquid latex is collected from the tree it needs to have a few drops of ammonia added to stop bacteria from spoiling it.
I think you’re following all the steps that are important … test for comfort, test for support, know what’s in your mattress to make meaningful comparisons, ask good questions, and deal with good and knowledgeable people … and you are doing all of these already
Phoenix