Hi LookingNow,
Combination side / stomach sleeping is a very difficult combination because the needs of stomach sleeping (thinner firmer comfort layers) are the opposite of the needs of side sleepers (softer thicker comfort layers) on the same support system so finding the right combination of even support/alignment under the different parts of your body with the conflicting needs of pressure relief and the different pressure points with side sleeping and stomach sleeping can be a challenging “balancing act”. In general … it’s usually most effective to use “just barely enough” thickness and softness to provide the pressure relief you need on your side so that there is less risk of sleeping in a swayback position and developing lower back pain from comfort layers that are too thick and soft when you sleep on your stomach.
Post #2 here and the topper guidelines it links to can help you use your actual sleeping experience on the mattress by itself to decide on the thickness and softness of a topper that may work best for you.
It’s possible that you may do best with a topper that is both a little thinner (to keep you closer to the support layers and in better alignment when you are on your stomach) and a little softer (for pressure relief on your side) than what you currently have.
“Pushback” is actually a misnomer and has little to do with pressure relief. All materials “resist” pressure (regardless of how resilient or springy they are) and the resistance of a material increases as you sink into it more deeply. Even memory foam which has no “pushback” resists pressure and becomes firmer as you sink into it more deeply. When you are lying on a mattress any “upward” pressure of a foam or innerspring is in equilibrium and balanced by the “downward” pressure of that part of your body and there is no longer any direction of the pressure … only the pressure itself. In other words … both the “pushback” of a material and the “push down” of your body weight are in balance and all that’s left is the amount of pressure on a particular part of your body.
The key factors that determine pressure relief are the softness (ILD/IFD) of the comfort layers, the thickness of the comfort layers, the compression modulus of the comfort layer materials (how quickly they become firmer as you sink into them more deeply) and the point elasticity of the material (how well it conforms to your body shape and redistributes pressure across the surface of your body). There is more about so called “pushback” in post #2 here and more about the factors that work together to relieve pressure in post #4 here.
All the layers and components of a sleeping system (such as a mattress topper combination) act together and affect all the other layers and components to some degree so it’s completely normal that a topper that works well on one mattress may not work as well on a different mattress.
Different types of latex have a different compression modulus and some types of latex are more point elastic than others even if they are the same thickness and ILD so the type of material can have an effect on pressure relief and alignment yes but using complex specs to decide on a topper (even if they are available and if the ILD between materials is consistent which is often isn’t) would be much too complex to use them to decide on a topper. I would tend to use the topper guidelines I linked earlier.
I would also be cautious with a 3" topper of 19 ILD latex which could be risky as a topper for a stomach sleeper because it would have a higher chance of being too thick and soft for stomach sleeping. What works well for one person can be completely unsuitable for someone else. I would also make sure you use a suitable cover for a topper because using a thinner mattress protector instead of a cover that is designed to be used as a mattress or topper cover can increase the exposure of the latex to oxidation from ozone or ultraviolet light or some of the other substances that can harm the latex (see here) and shorten the useful life of the latex.
Phoenix