Hi Kavi,
If your mattress is still in very good condition and there are no soft spots or sagging (virtual or visible) in the mattress then a topper can be a good idea if all you need is some extra pressure relief and comfort.
How he feels about a latex topper will probably depend on how he feels about a more highly resilient material and also on the thickness and firmness/softness of the topper. Apparently the Ellenstone used memory foam in at least part of the comfort layers and the slow response “feel” of memory foam is a very different “animal” from the fast response of latex (see post #2 here). The only way to know ahead of time would be for him to test some mattresses that use latex comfort layers locally so he can get a sense of how latex feels in very general terms although this won’t tell him how a specific topper will feel for him on top of your mattress.
Featherbeds and fiberbeds can add a little bit of “cush” or surface feel to a mattress but they compress so easily that they just add a little bit of cushioning directly under pressure points and don’t do a great job at redistributing pressure along the larger surface area of the body or providing support under the more recessed areas of the body (such as the small of the back for back sleepers or the waist for side sleepers). They are also a higher maintenance item because they need to be fluffed up on a regular basis because they pack down and compress with use unlike a more resilient foam topper.
Stomach sleeping is also a very risky sleep position and if a mattress has comfort layers and/or toppers that are too thick and soft it can cause issues with sleeping in a swayback position which can lead to discomfort or pain in your lower back. Stomach sleeping an also lead to neck pain because your neck is turned when you sleep on your stomach and I would also make sure that you use a very thin pillow or no pillow at all when you sleep on your stomach so that your head and neck are also in good alignment. When stomach sleeping is one of your sleeping positions then it becomes more important when you are choosing a topper that you choose “just enough” in terms of softness and thickness to relieve pressure on your side and no softer or thicker than “necessary” so that the risk of stomach sleeping is less.
There isn’t a forumula that can be used to choose a topper because there are so many variables involved but post #2 here and the topper guidelines it links to can help you make the best topper choice based on your assessment of how much more softness/thickness you need.
Phoenix