Hi gibson,
I can certainly speak to the quality of your choices but there is no way for me to know how they will “fit” in terms of PPP (Pressure relief, Posture and alignment, and Personal preferences). The only way to know that for certain is to try it.
2.8 lb HR polyfoam is a very high quality material with a higher resilience and support factor than conventional foam. Even lower quality base foam would probably last 10+ years (depending on the thickness of the layers above it and how much you were compressing the base foam) because it’s usually the comfort layers that are the weak link of a mattress … not the base layers. The advantage of higher quality base layers is more in terms of performance and how they interact with the other layers than in terms of durability although they would have some influence on durability as well.
Many of the Stearns & Foster mattresses that have “latex” in the labels can be surprising what they really contain. In many cases they use what they call “smart latex” which is synthetic Dunlop latex and lower quality than the more typical 100% natural Dunlo latex. In other cases they use fairly thick layers of polyfoam in the comfort layers along with the latex and people who buy them don’t even realize that what they are sleeping on polyfoam more than they are sleeping on latex.
In theory … a 2" latex topper over HR polyfoam can make a good design but the specific details are what would be important such as the ILD of the base layer and the ILD of the 2" topper and how they interacted together and with your body in all your sleeping positions. This is the part that your own experience is really the only way to know how suitable that particular layering will be. This also means of course that unless you have tested a specific combination of materials in person … your options in case you make the wrong choice are also important.
when you are choosing combinations that are unknown to you in terms of how they will feel and perform … it’s usually “safer” to choose slightly firmer over slightly softer because you can always add some thickness or softness to a comfort layer but it’s much more difficult to firm up a mattress that is too soft.
Vancouver has some good choices available and the better ones I’m aware of are listed in post #2 here and may be worth including in your research.
Phoenix