Hi attavan,
Both of the manufacturers you are mentioning use high quality materials and are great value but the choosing the specific design that is most suitable for you is always best left to either your own personal testing on similar mattresses that may be available locally or to more detailed discussions with each manufacturer. Post #2 here has more about making comfort choices and has some links to some of the 'theory" involved but the actual manufacturers know more about their own designs and materials than anyone and outside of your own personal testing are in the best position to help you make the most suitable comfort choices.
You can read a little more about some of the options that can help accommodate weight differences in the first part of post #2 here.
You can also read a little more about some of the potential benefits of a thicker mattress for higher weights in post #14 here.
Post #2 here may also be of interest.
Heavier weights will of course tend to sink in more deeply into any material and firmer comfort layers will feel softer because of this than they would for lighter weights so your “medium to firm” would likely “feel” similar to you than a softer layer would feel to your wife. Of course firmer support layers would also do a better job of “stopping” the heavier parts of your body from sinking in too far and help maintain neutral alignment for your spine in all your sleeping positions.
I would tend to just “scan” the information linked in the previous posts and use it as a reference so you can have more meaningful discussions with each manufacturer rather than “study” it or use it to try and design your own mattress based on “theory” which can quickly lead to “information overload”
Phoenix