Hi sleepymath,
Welcome to the Mattress Forum! 
Being a stomach sleeper primarily and also of a higher BMI, it would make sense to focus on something that is in the “firmer” range of surface comfort.
A higher BMI presents special challenges and generally requires firmer materials (in the support layers especially). This could be firmer latex or innersprings (the type of support component would be a personal preference and in the right design either could be suitable) or even a zoned construction. The same overall guidelines apply with higher weights though that PPP (Posture and alignment, Pressure relief, and Personal preferences) along with using high quality durable materials that will maintain their feel and performance for longer periods of time are the way to make the best choices. Heavier people in general will need firmer and thicker comfort layers and firmer support layers than those who are lighter and because no materials will last as long with much higher weights the quality and durability of the materials and components is even more important than normal. I wouldn’t “rule out” any types of mattress and base your choices on your own personal testing. Post #3 here has more information and suggestions about heavier weights that is worth reading.
The key will be finding componentry that will be of appropriate quality for your specific situation, which will then give you the best chance at have a successful comfort life, so I would always make sure that you find out the information listed here so you can compare the quality of the materials and components. Those in a higher BMI range want to be especially prudent in the choice of their components, and there is more information about selecting a mattress in the durability guidelines here.
Firmer and more resilient materials can help avoid the feeling of being “stuck”, so a firmer, higher density polyfoam or latex configuration for the upper comfort layers could be appropriate to consider.
In very general terms … the materials, layers, and components of a sleeping system that are closer to your skin will have a bigger effect on airflow, moisture transport, and temperature regulation than materials, layers, and components that are further away from your skin and softer mattresses or foam toppers will tend to be more “insulating” and for some people can sleep warmer than firmer versions of the same material. There is more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here that can help you choose the types of materials and components that are most likely to keep you in a comfortable temperature range. You’d probably wish to avoid softer materials that allow you to sink in too deeply and insulate you more, and also more than likely want to avoid visco-elastic memory foam in the uppermost layers.
As for edge reinforcement, most latex mattresses will not have a specific edge reinforcement system. While the edge will feel “softer” when sitting upon the product, it will be resilient and you can still sleep quite close to the edge of an all-latex mattress without “rolling off”, due to the supportive and point elastic nature of the latex. If you desire to choose a unit with an innerspring unit, many of the pocketed spring units commonly used in the “hybrid” latex mattresses either have a firmer polyfoam edge reinforcement system, or contain firmer springs along the perimeter.
This all depends upon your own personal preferences and sensitivities, and also what type of innerspring mattress you’re currently used to. The layers closest to your skin will have the most dramatic impact upon your comfort, so whether or not your choosing an all-latex mattress or a hybrid, if latex is used on the top of the mattress and your old mattress didn’t use latex in the uppermost comfort layers, it will be a change in comfort. With that being said, using a strong pocketed spring unit with latex on top will be “closer to home” of what you’re used to than switching to an all-latex mattress. Post #28 lists some of the differences between latex versus springs.
My general advice would be to avoid the major brands such as Sealy/Stearns & Foster, Simmons, and Serta, as they all tend to use lower quality and less durable materials in their mattresses than most of their smaller competitors that will tend to soften or break down prematurely relative to the price you pay which is why I would generally suggest avoiding all of them completely (along with the major retailers that focus on them as well) regardless of how they may feel in a showroom along with any mattress where you aren’t able to find out the type and quality/durability of the materials inside it (see the guidelines here along with post #3 here and post #12 here and post #404 here). If you do decide to purchase from one of these brands, I would recommend selecting something using a low amount of low-density foam and something that is “firmer” in surface comfort, using the guidelines as expressed in the mattress shopping tutorial here.
If you do decide to look online, I would consider using the expertise of the members listed in post #21 here who are all very experienced and knowledgeable and specialize in providing the type of help and guidance on the phone that can help you make good choices. There are a wide range of latex options included in the choices there and I believe that all of them compete well with the best in the industry in terms of their quality, value, service, and transparency. There is also a list of online mattress sources for Canadians in post #21 here.
Phoenix