Hi awoods,
While it may turn out to be true that you need a thicker comfort layer … the “comfort zone” or what I have sometimes called the “critical zone” isn’t the same thing as the thickness of the layers on top of the mattress and will have more to do with the relative firmness of the top few inches of your mattress combined (regardless of the thickness of any individual layers). There is more about this in post #4 here. If it did turn out that your shoulders don’t sink in enough to provide good pressure relief then this would be a case where adding a topper can provide any “fine tuning” that would be necessary if you don’t have any other “fine tuning options” such as a thicker top layer, a softer top layer, a different quilting pattern in the mattress cover, or other options such as a different pillow or a different mattress protector that can improve the pressure relief under the shoulders.
There is more about dust mites in post #2 here but in order for dust mites to multiply and thrive they need a source of food and a source of moisture. Their food comes primarily from skin flakes and a mattress protector (or in some cases a mattress encasement for those that are much more sensitive and/or have known dust mite allergies) would greatly reduce the amount of skin flakes that enter your mattress and “feed” the dust mites. The other is a source of water which they “drink” by absorbing moisture from the air or environment around them. Since coils are more breathable and have higher airflow than foam and ventilate well … they would be less likely to retain the moisture levels that are needed by any dust mites in the mattress. Although it’s true that pocket coils that have fabric pockets will have less ventilation than innersprings that don’t use fabric pockets … it’s unlikely that ventilation would be an issue with any type of innerspring (see post #2 here).
In terms VOC’s and offgassing of the foam surround … the large majority of people would be fine with polyfoam that was either made in North America and/or was CertiPur certified. For the very small minority that were more sensitive to any specific VOC’s than CertiPur tests for (you can see the testing limits here*) because of unusual sensitivities such as MCS (multiple chemical sensitivities) or other health conditions … then they would probably also be sensitive to polyfoam used in their furniture as well and may be better off to avoid polyfoam altogether.
ADMIN NOTE:*Always check CertiPur site for the latest guidelines available
That’s a good idea but again … I would keep in mind that the “critical zone” and the depth of a pressure relieving cradle will also depend on the type, firmness, and thickness of the comfort layer along with the softness of the next few inches of materials or components underneath it. If a mattress you test has a thicker or softer comfort layer but uses firmer layers or components underneath it then it may not be a good reference point for comparison because it could still feel firmer to you than a mattress that uses a thinner comfort layer.
Phoenix