Hi paisley,
The cover is probably at least part of the explanation …
As you can see it has fairly thick polyester clusters that would separate you from the memory foam and change the way it responds to body temperature and pressure and make it firmer. A thin stretchy cover that will keep you directly on the memory foam would probably do better for you and let you sink into the memory foam more.
6’’ of memory foam would be very risky (memory foam continues to get softer over the course of the night and this could lead to trading your pressure issues for alignment issues). The latex topper would be well worth trying folded over into a 2" layer without the memory foam although it may be a little on the thin side and you may do better with closer to 3". It’s Dunlop and probably synthetic so it would likely be a little firmer than soft talalay although they don’t provide any density or ILD information so it’s not really possible to know for sure.
This would be helpful to get a sense of the overall feel of latex (beyond just the convoluted topper you have tried). I would also try to find out the type and firmness or density of the latex you are testing and to get a sense of the firmness of the mattress or layers under the topper because all of this will make a difference in how a topper feels and performs for you. the closer the underlying mattress is to yours the closer you will have a sense of how the topper will work on your mattress.
The first one is natural Dunlop, the second one is natural Talalay, and the third one is blended Talalay. In other words they are all different types of latex. You can read more in this article and in post #6 here.
Some vendors also have allow returns or exchanges so you can exchange for a different firmness level if your first choice isn’t the best one for you.
No … one firm non flexing base or foundation will feel the same as a different type that is also firm and non flexing.
This one looks more flexible on the surface so it may make some difference. Thicker mattresses and lighter weights would notice less effect and thinner mattresses and heavier weights would notice more of an effect so it’s probably worth a try to see if it makes a difference for you.
Phoenix