Hi juveman.
Welcome to our Mattress Forum! 
No problem … I am used to “hijacked” threads … it may be like this for a little longer until we finish working on the back end on the new features.
Thank you for your appreciative comments, we enjoy doing things the right way.
Congratulations on your weight loss! Having only a few pounds less is much better all the way around … both sleepwise and healthwise.
High 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. Because the combination of your 35 BMI with prone and back sleeping positions the same overall guidelines would apply especially to you in order to achieve the needed 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. All in all, regardless of the materials you prefer I would make sure to use something using appropriate, firmer, and higher density foams.
Post #2 here has some generic guidelines for different body types and sleeping positions, and post #14 here has more about the benefits of thicker comfort layers and thicker mattresses (most of these are in the tutorial post but I thought I’d highlight them here as well.
Higher BMI ranges will need more durable materials and components in a mattress and in a BMI range of 30 or higher I would include any 1.8 lb polyfoam or 4 lb memory foam as a “lower quality/density” material (relative to a higher BMI only) and minimize their use to a total of “about an inch or so or less” in the mattress.
Polyurethane foam: If your mattress is one sided then I would look for 2.0 lb per cubic foot density or higher. If the mattress is two sided then I would use a minimum density of 1.8 lbs per cubic foot or higher.
Memory foam (or gel memory foam): If your mattress is one sided then I would make sure that any memory foam is at least 5 lb per cubic foot. If the mattress is two sided then I would use a minimum density of 4 lbs per cubic foot.
A mattress needs to have deeper layers that are “firm enough” to stop the heavier parts of your body from sinking down too far and make sure you sleep with your spine and joints in good alignment and upper layers that are thick and soft enough to “allow” any pressure points such as the hips and shoulders to sink down far enough to relieve pressure points in all your sleeping positions as well but “firm enough” and “soft enough” can vary widely from person to person.
There is also more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel”.
You can read about the Novosbed product specifications here, Based upon the information you presented here, I would imagine that Nest would recommend their Luxury firm, but you’d definitely want to have a more detailed phone conversation with them. Both Nest Bedding and Novosbed are vetted members of this site which means that I think very highly of them and that I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency. Based on your conversation with them and your own careful assessment of suitability for your higher weight and prone sleeping position, I certainly wouldn’t hesitate to purchase a mattress from either of them.
I would agree with you that the firmer options may be better for you perhaps more thickness to play with as well.
As this is such a personal choice and only you can feel what you feel on the mattress I could not tell you if tell if the memory foam choice would be appropriate and I would be concerned about sinking into it too deeply when on sleeping on your stomach.
Generally speaking, the thickness of a mattress is a byproduct of design, but people that have much higher body weights or larger body types may choose more than the “average” thickness and may prefer the feel and extra adaptability of say 12" of latex. Thicker mattresses can also use firmer materials because thickness and softness are very related and work together. Thickness and softness work together and because thicker layers (or mattresses) can have a greater range of compression and are more “adaptable” … it’s also possible to use firmer top layers in a thicker mattress and still have good pressure relief because of the greater range of compression of the thicker mattress which can create a mattress with a firmer “surface feel” but that still provides good pressure relief and adapts well to the body contours.
Hopefully, this gives you enough information to help with your research.
I would be interested to hear back from you to learn what you decided and I or any other Expert Member of the site would be glad assist you with any questions that you may have.
Phoenix.