Hi farmdevil,
Needless to say … he does “know his stuff”
The density of polyfoam is the single biggest factor involved in the durability of the material but it has little to do with firmness and any density of polyfoam can be made in a wide range of firmness levels.
Polyfoam can range from a low quality/density material that isn’t very durable at all to a high quality/density material that is very durable depending on the density. As you can see in the durability guidelines here … 1.8 lb polyfoam would be a good quality and durable material that would certainly be suitable for those that are in more average weight ranges (around the lower 200’s or less).
All the layers and components in a mattress (including the cover and any quilting materials) will have some effect the feel and performance of every other layer above and below it and the mattress “as a whole” to different degrees so what you feel on a mattress is the combined effect of all the layers and components in the mattress rather than the effects of just a single layer or component but it’s not possible to know for certain how any specific mattress or the combined properties of a particular combination of materials and components will interact with your specific body type and sleeping style or whether it will be a good “match” for you in terms of “comfort”, firmness, and PPP (Posture and alignment, Pressure relief, and your own Personal preferences) until you have tested it or slept on it in person.
In very general terms … the properties and firmness of materials and components that are closer to the top surface of a sleeping system will tend to have a bigger effect on the overall “feel” and firmness of a mattress than materials that are deeper in the sleeping system, thicker layers or toppers will contribute more of their feel and firmness to the overall sleeping system than thinner layers, and a thinner layer would “allow” more of the feel and properties of the layer(s) underneath it to “come through” than a thicker layer.
An additional 1" layer is relatively thin so it would have less effect on the feel and performance of the latex layers below it than a thicker layer but the “feel” of the mattress will also change to some degree with any change in firmness as well (which of course is what you are looking for).
You are the only one that can feel what you feel on a mattress so the only way to know for certain whether any mattress or any adjustment to a mattress will be a good “match” for you in terms of “comfort”, firmness, and PPP will be based on your own careful testing or your own personal experience when you sleep on it but they would be the best source of guidance because they are much more knowledgeable about their mattresses and their comfort adjustments than anyone else (including me) and their suggestions would be based on many years of experiences and the “averages” of many other customers they have helped that are in a similar situation to your own so their knowledge and guidance would give you the best chance of success.
It’s unfortunate that you are too far away to bring the mattress into their factory because their comfort adjustment is free for those that are in their local area and bring their mattress to the factory.
Unfortunately your question isn’t really possible to answer because there are too may unknowns, variables, and complexities involved with how different body types and sleeping styles interact with a specific mattress design or mattress/topper combination to know for certain and the only way to really know will be based on your own personal experience.
If you add a relatively thin (1" to 2") and firmer topper you would lose some of the softer surface feel that comes from the quilting layer and the topper would also move more independently and “act” softer than it would if it was a layer inside the mattress cover and since there would also be thicker layers of soft foam underneath the firmer topper they could end up as a transition layer that was too thick/soft for your body type and may still allow your hips/pelvis to sink down too far when you are on your back so it may only provide partial or temporary relief.
Having an additional inch of foam inside the mattress cover will make the cover a little tighter and compress the other foam layers a little more and make them slightly firmer as well.
Having said that … if you buy a topper from a supplier that has a good return policy with either little or minimal costs involved then it would certainly be worth trying. The better online sources for toppers I’m aware of are listed in post #4 here and if you limit your options to the ones that have a good return policy there would at least be little risk in trying it.
If you decide to try a topper and you are getting close to the end of your 100 day trial then it may also be worth asking them if you can extend it for a short time so you have time to purchase a topper, have it delivered, and try it out for a while to see how it works.
I don’t know the adjustment options they have available but it may also be worth asking if they can replace the 2" latex layer with a slightly firmer latex layer with the same thickness but I don’t know if they have firmer latex available (many manufacturers only carry a limited range of firmness levels).
Phoenix