Hi rolandtorres,
I don’t see a Sensus 9 on their site … only a Sensus 8 and a Sensus 10. Based on your description though I’m assuming you mean your mattress has 3" of Sensus on top over 2 x 3" layers of polyfoam which is the description of the Sensus 8 even though the layers add up to 9" instead of the 8 they mention in the description).
The first step is to make sure you have clarity about exactly what you are looking to change.
If your issue is “primary support” (the type of support that stops the pelvic girdle from sinking in too far) … then this is usually a matter of fine tuning the deeper layers … not the top layers. An example of firming up the support layers would be to exchange the polyfoam layers on the bottom so that the firmer layer was closer to your body.
If your issue is “secondary support” (the type of support that fills in the gaps in the sleeping profile in all your sleeping positions such as the recessed lumbar curve or the waist or controls the distance of “travel” before your heavier parts reach the firmer support layers and are “stopped”) … then this is usually a matter of fine tuning the thickness and/or softness of the comfort layers. This could be done with a topper if you need to add to the thickness or softness.
If your issue is pressure relief … then this is also usually a matter of fine tuning the thickness and softness of the upper layers of the mattress. Once again … a topper can certainly help here.
All of these are interactive and each change will affect the others as well but this is the general idea of how to control the balance between primary and secondary support and pressure relief.
When you are fine tuning a mattress with a topper … it’s important to make sure you have identified exactly what you are wanting to change (primary support, secondary support, or pressure relief, or even just “feel”) and then using your best judgement (in combination with the guidance and help of the people who make the mattress or sell the topper because they have the best knowledge about the products they sell) about how it will affect the other qualities of the mattress so that you don’t end up fixing one issue and introducing another one completely. Usually changes that are “just enough” to improve what you want to change is the key to making changes that will have the least possible effect on the other qualities of the mattress and the balance between support and pressure relief for your particular body type and sleeping style.
So if your issue is primary support … then making the deeper layers firmer (such as re-arranging them) could be the “best” answer.
With the other two … a topper could help.
As far as I know and based on the Tempurpedic website information and other descriptions such as here … the Rhapsody uses 1.2" of their HD memory foam which is 7 lbs density on top of a 2.8" layer of their regular Tempur material which is 5.3 lbs. The Tempurpedic 7 lb memory foam by most standards (keeping in mind that memory foam responds to many variables including heat, humidity, pressure, and time) is also softer than their “regular” Tempurpedic memory foam. I would also keep in mind that other factors such as the speed of response of denser memory foams and the time it takes for them to become softer can also affect the perceptions of different people about how firm a specific layer feels to them. For example if you “slap” honey it will feel firm but if you press into it slowly then it will feel softer. Tempurpedic also doesn’t mention the IFD of their base layers which can also make a difference but it would be reasonable to assume that they are somewhat similar to what you have.
If you are looking for layers that are closer to the Rhapsody in terms of density and layering … then an additional 1" or so of 8 lb memory foam would be closer than what you have (this would give you 4" of memory foam in total of similar density which is the same as the Rhapsody but slightly different in layer thickness) but I would also keep in mind that different types of memory foams have different properties … even if the density is the same. Using density and layer thickness alone to “approximate” another mattress may not lead to your mattress having the same feel and performance as a mattress that uses memory foam of a similar density or even layer thickness but has different properties … although it would most likely be “closer” than what you now have. You can read more about the variations in the properties of different memory foams in post #8 here and post #9 here.
With Tempurpedic … the 4 lb is generally considered to be the softest followed by the 7 lb HD and their regular memory foam is the firmest although they also have variations of their regular memory foam in terms of “softness” (which is not that meaningful a term in the case of memory foam because of the variables that contribute to its firmness). This is similar to the 8 lb Venus being softer than the regular 5 lb Sensus.
So all of the options you mentioned seem well thought out and it seems you have correctly identified the tradeoffs between them (with the exception of using firmer support layers for better support and using 2" for your topper height instead of 1" which would be closer to the Rhapsody).
I think that the least “desirable” of your options would be #4 because it is nothing like any of the layering you are familiar with or have tested so it would be a complete unknown in terms of feel or performance. this doesn’t mean it couldn’t work for you … only that it has the most unknowns.
Option #1 would change secondary support and pressure relief to different degrees depending on the firmness of the latex you were considering. This would also be outside of your testing experience as well because of the differences between latex/memory foam hybrid comfort layers and comfort layers that used only memory foam. You may also need to change the cover thickness if you are adding foam inside the mattress instead of on top as a topper. This would lead to a fairly different mattress from the one you have but it may also be worth considering some latex over the memory foam as an option (it creates a more responsive surface and slows down the response of the memory foam underneath and has a different feel which I personally like but others don’t).
I would choose between the options based on clarity about exactly what you want to change and which of the tradeoffs and the different types of fine tuning are most important to you and based on the topper guidelines in post #8 here and the other posts it links to. It would also depend on how confident you are about some of the more “unknown” options you are considering. I would also keep in mind that an extra inch of 8 lb memory foam would be closer in terms of specs than the 2" you are mentioning and if you use a thicker layer than this, especially with 4 lb memory foam, then you are moving into Tempurpedic Cloud territory such as the Tempur Cloud Supreme which uses 2" of 4 lb memory foam over 2" of 5.3 lb memory foam (although yours would have an extra inch of 5 lb memory foam in the second layer which would give you more memory foam to sink into over the course of the night before you reached the firmer support layers so it would have more alignment risk).
So while I can’t tell you what to choose … hopefully this will give you a greater sense of the differences between your options that you can use to “match” to what you want to accomplish and the effect each one may have for both of you.
Phoenix