Hi BedBug,
Thanks for the link.
The “down alternative” mattress pad you are using can certainly affect the “surface feel” of the mattress but it can also reduce the amount of heat that reaches the memory foam which can affect the firmness of the memory foam underneath it as well as it’s ability to contour to your sleeping profile (both of which will affect the sensation of “softness”) so this type of topper on a memory foam mattress can create a “feeling” that is both softer (the surface "feel) and firmer and less pressure relieving (from the memory foam layers underneath) at the same time.
If you like the “feel” of sleeping directly on memory foam and it’s ability to contour and “shape” itself to your body profile and need a little more “comfort” or pressure relief then a thin memory foam topper may make a better choice. A thinner mattress pad may also allow more heat to reach the memory foam.
As I mentioned your mattress appears to be a good match for you in terms of PP (Posture and alignment and Pressure relief) and it certainly uses high quality and durable materials but you may need a little more memory foam so that the “surface feel” is closer to your preferences. There are also some suggestions in post #2 here about a new memory foam mattress that is too firm that may also be helpful.
Phoenix