Hi Reb_enfilade,
Any topper can increase the useful life of a mattress underneath it to varying degrees (depending on the specifics of the mattress and the topper) because it will take up some of the compression forces that are the main cause for foam softening and breakdown in the upper layers of a mattress. Since a topper will generally soften or break down faster than the mattress underneath it … a topper also has the advantage that you can replace it without having to replace the entire mattress.
More important than making the mattress last longer though is making sure that a mattress/topper combination is a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) because there is little point in having a long lasting sleeping system if you can’t sleep well on it. The main reason to choose a topper would be to add additional pressure relief and comfort to a mattress that is otherwise too firm and any additional longevity would be a side effect of the process.
There is more about trying to “match” one mattress to another one in post #9 here but the Genius and the Savant are two completely different mattress designs with different combinations of materials so you won’t be able to “match” the Genius to the Savant unless you were to remove the top layers in the Genius (the layers over the support core which are the same in both) and replace them with the same type and thickness of materials in the Savant which of course isn’t possible.
Rather than trying to “match” another mattress … I would focus on choosing a topper that in combination with your mattress has the best chance of providing you with the additional softness and pressure relief that you need and I would use the information in post #2 here and the topper guidelines it links to to help you use your actual sleeping experience on the Genius to help you decide on how much additional softness, thickness, and pressure relief you need so that your sleeping system will be a good match for you in terms of PPP. Because there are so many variables involved and because the only way to know for certain that a mattress/topper combination will work well for you is based on your actual sleeping experience, it can sometimes take some trial and error to choose a topper that is the best match for a specific mattress and person so the return and exchange policy for a topper purchase may also be an important part of your choice so that if the topper you choose doesn’t work as well as you hoped it would you still have the option to exchange it for another one.
If you seem to prefer the feel of sleeping on memory foam (based on the mattress you purchased) … then it would make sense to purchase a memory foam topper so that your sleeping surface has the “feel” that you prefer and it may also be worth considering a gel memory foam which will tend to have a faster response than most non gel memory foams.
Phoenix