Hi amym,
Post #2 here has links to some generic guidelines for different body types and sleeping positions but it’s generally better to use these as generic guidelines only because each person’s needs and preferences can be very different and the guidelines aren’t specific to any individual person. The mattress testing guidelines in the tutorial post have the highest chance of finding the best match in terms of PPP.
In general terms … stomach sleepers need firm support with thinner comfort layers to prevent the pelvis from sinking in too deeply which can lead to sleeping in a swayback position and the back issues that can go with it. Stomach sleeping is the most risky of all the sleeping positions in terms of alignment and back issues. It can also be a good idea for stomach sleepers to use a thin pillow under the pelvis to help prevent alignment issues.
Thicker layers of memory foam can be particularly risky because it can continue to soften over the course of the night which means that you can start off the night in good alignment but be out of alignment when you wake up in the morning. At the very least it would be a good idea to use thinner layers of memory foam with a more resilient material underneath it but in your case it would probably be better to avoid it completely just to be on the safe side.
Even a 4" mattress from Ikea may be a good choice for an exclusive stomach sleeper although it may not work as well for a sleeping partner that sleeps in other positions and there may also be other mattresses that work better for you … especially if you also sleep in other positions as well … because a mattress that thin can also be quite firm.
If you follow the steps in the tutorial one by one you will have very high odds of making a great choice 
Phoenix