hi Savasana,
The one thing that seems clear from your preferences on other mattresses … even though they are somewhat apples to oranges in terms of materials (memory foam is very different from latex) … is that you like firmer than average layers for typical side sleepers.
I can certainly understand the Bed in a Box being too “mushy” for you because it has quite low density memory foam (it’s actually about 3.5 lbs density and I normally don’t suggest less than 4 lbs, especially for weights over 200 lbs where 5 lbs would tend to be more appropriate unless the layers were thinner although they do use high quality base foam).
The contour select is a firmer memory foam mattress and the Genius uses soft memory foam but the polyfoam layer under it is very firm and it would “come through” the gel memory foam layer. It wouldn’t stay firm for long though because the polyfoam layer is also very low density and will soften fairly quickly (see post #2 here). The Elsfjord is also very firm and because it is synthetic latex (has less elasticity than natural latex) and also very thin it wouldn’t conform nearly as well as better quality latex in thicker layers. I don’t think it would be suitable for you but it does confirm that you are OK with firmer than average mattresses.
Given your preferences for side sleeping and firmer mattresses … you would probably do best with a comfort layer in the 28 - 32 ILD range (whatever their number is for this) and he may be better with the firmer and you may be better with the softer. they also have an option where they can make the quilting tighter which creates an “in between” firmness level and this may be an option (the softer 28 with the firmer quilting). The biggest “risk” would be with your partners stomach sleeping and he may need a pillow under his hips with a layer of latex that is this thick to prevent sleeping in a swayback position (stomach side sleeping is the most difficult and “risky” sleeping position combination and the thinnest/firmest possible comfort layer that is “just enough” for pressure relief on the side is usually best for alignment on the stomach.
With all of this … I would also defer to any suggestions that Chuck makes because he has a customer base that he can use as a reference point and is also more knowledgeable about all the finer details of their mattresses than I am so use this as a reference and take his suggestions as having more weight.
Phoenix