Hi gadda,
Welcome to the Mattress Forum! 
You’re welcome!
As you’ve already read the mattress shopping tutorial (good job!), you’re aware that all I can help with is “how” to choose, as it’s not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best “match” for you in terms of “comfort”, firmness, or PPP (Posture and alignment, Pressure relief, and your own Personal preferences) or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or “theory at a distance” that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here). But I’ll try to provide some feedback based upon some of the information you’ve provided.
As you are in New York City, and it sounds as if you want to try out your mattresses in person, you may wish to visit a local retailer. Subject to first confirming that any retailer or manufacturer on the list that you wish to visit is completely transparent (see this article ) and to making sure that any mattress you are considering meets the quality/value guidelines here … some options or possibilities I’m aware of in and around the the New York City area are listed in post #2 here.
When sleeping in the prone (stomach) position, a “firmer” surface comfort is usually desirable, combined with strong deep support, to help with good alignment and also to minimize the accentuation of the lordotic (forward) curvature of the lumbar (low back) region. Post #2 here and this post cover in more detail different sleeping positions.
Something using higher density polyfoam or a latex (not too plush) on top, whether a hybrid or not, could certainly be a good choice, and these materials would be more “resilient” and you wouldn’t sink in as deeply. Post #2 here has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort”, firmness, and PPP (Posture and alignment, Pressure relief, and your own Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for.
That style of comfort would tend to be recommended for most prone sleepers, so you’re off to a good start. The only reliable way to assess the “safety” of different materials in more general terms is based on lab tests and the certifications they have for harmful substances and VOCs (regardless of whether they are organic or natural or synthetic) so that you have some assurance than the VOCs are below the testing limits for the certification. If the materials in a mattress or the mattress itself has a reliable “safety” certification then for most people they would certainly be “safe enough”. There is more about the different types of organic and safety certifications such as Oeko-tex, Eco-Institut, Greenguard Gold, C2C, and CertiPUR-US in post #2 here and more about some of the differences between organic and safety certifications in post #2 here and there are also some comments in post #42 here. CertiPur* tests for harmful substances and VOCs in the polyfoam and memory foam used in mattresses.
If after reading through this information and visiting some local stores you come up with a “short list” of products and supply their specifications, I can do my best to serve as a “sounding board” for you on those items.
Phoenix