Hi AnalogJ/Jeff.
Great to have you back! 
Good to hear that you are happy with the decision you made 6 years ago and all the help you got from our mattress forum. Too bad that started to breakdown (probably from the wear and tear that comes with high BMI sleepers) but I am glad to see that you are ready to upgrade and looking at some good mattress options. I am seeing that you are making good headway with your choice and getting some input from our subscribers that sleep on one of the options you are considering.
You seem to be almost ready to pull the trigger so so it may be a good time to throw a few cents worth of reinforcement opinions.
(9.8") Vispring Coronet … Vi-Spring certainly makes some exceptional hand-built and tufted mattresses that use high-quality materials and components (pocket coils and natural fibers) but as you probably know they are in a much more premium budget range than many other mattresses that also use natural materials. With this option, it’s good that you can customize comfort/support before the purchase according to your personal sleep preferences and statistics. The downside of it is that if the match does not turn out as well as you are hoping for any of the sleepers you don’t have alternative options.
Layers that are closer to the top sleeping surface will have the greatest impact upon comfort and sleeping temperature (including any mattress pad, sheets, and linen). I am not sure if you came across some of our posts that discuss temperature regulations issues, but you can read more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here more about tracking mattress temperature regulation issues potential causes ~ Post #2 here (at leastpost #29 about temperature regulation and mattress microclimate to the degree possible for a specific mattress) and the posts it links to that may be helpful. You may also be interested in the information in .
The natural fibers in all the options you are looking at, allow for airflow and humidity control which translates into better temperature regulation, as does the type of ticking (cover) used: such as wool, silk, cotton or viscose or even some of the more breathable synthetics which wick away moisture and ventilate better and humidity control is a key part of temperature control.
If your wife is mainly a prone sleeper, she’d need the thinnest comfort layer … back sleeping is in the middle, and side sleepers like you need the thickest comfort layer. It is rare that anyone … even a side sleeper … would need more than 4" in a comfort layer. I’d recommend that you weigh your comfort/support choices well as stomach sleeping is a common source of back issues as stomach sleepers tend to sleep in a “swayback” position, especially if their comfort layer is more than an inch (or at most two) or if their support layer is too soft. You don’t mention your wife’s BMI but If there is a large disparity between your weights, that would be another factor to consider in choosing a mattress that will be both comfortable and durable for years to come.
EOS mattresses come in 2 configurations:
[indent](14" +) EOS PILLOWTOP (8"support coils + 2 of the 3" comfort layers)
[indent](Detachable zippered pillowtop
• quilt (organic cotton & wool batting)
• 3" organic Dunlop latex comfort layer
Base mattress
• 3" organic latex comfort layer
• 8" encased coils with edge support (wrapped in organic cotton fabric)
• organic cotton batting + bottom encasement (organic cotton & cotton fill + solid brass zipper)
Firmness choices:
–Latex (extra plush, plush, medium, cushion firm and firm)
–Microcoil (extra plush, plush, medium and cushion firm) [/indent]
[/indent]
[indent]((11" +) EOS CLASSIC (8"support coils + 1 of the 3" comfort layers)
• Base mattress alternative of the above. [/indent]
Both options are customizable on either side of the mattress …as you say, the best solution for sleepers who vary in BMI and sleeping position is to go with a side by side layering. You are going definitely into the right direction with a firmer side for your wife, as you have a high BMI and need for some cushioning with your side sleeping, and if budget is not an issue, I’d probably opt for the Pillowtop version between the two EOC’s you are considering. (This being said the 11" can work as well but the 14:" + would give you more choices.) as far as the feel, need, and… personal preference goes. Because of the need to fine-tune with sleeper differences in mind I’d probably go for the EOC, and try to test it several times (different days if possible) before deciding to go with the microcoil option they have available… with EOC you should be able to fine-tune and exchange layers with their many offerings of X- plush, plush, medium, firm, and extra firm to get the right fit for both sides sleeping styles and BMIs. Either way… all your choices are between good and good which is the best position to be in. :).
Let us know what mattress is the final winner in your “sleep well” contest.
Phoenix