Hi smmimp14,
Unfortunately 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” or PPP 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).
If you are attracted to the idea of designing and building your own DIY mattress out of separate components and a separate cover then the first place I would start is by reading option 3 in post #15 here and the posts it links to (and option #1 and #2 as well) so that you have more realistic expectations and that you are comfortable with the learning curve, uncertainty, trial and error, or in some cases the higher costs that may be involved in the DIY process. While it can certainly be a rewarding project … the best approach to a DIY mattress is a “spirit of adventure” where what you learn and the satisfaction that comes from the process itself is more important than any cost savings you may realize (which may or may not happen).
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” that may be useful as well.
For those who decide to take on the challenge then I would either use the specs (if they are available) of a mattress that you have tested and confirmed is a good match for you in terms of PPP as a reference point or blueprint and try and “match” every layer and component in your reference mattress as closely as possible or use a “bottom up” approach (see post #2 here).
The thickness of a mattress is only one of many variables that can affect the feel and performance of a mattress but in higher weight ranges (or a higher BMI) the odds are higher that you may do better with a mattress that is thicker than lower weight ranges or a lower BMI (see post #14 here for more about the effect of thickness) but even this depends more on the specific design and combination of materials in the mattress and on how well your testing or personal experience indicates the mattress “as a whole” matches your specific needs and preferences in terms of PPP than it does on just the thickness itself.
It will also depend on your body type and sleeping positions as well because side sleepers may need more softness and contouring than back or side sleepers.
I would probably start with one additional layer which would most likely be an extra firm on the bottom then I would decide whether to add an additional layer based on your experience on your initial combination.
If you wanted to start with a softer combination as your initial combination then I would probably consider another medium layer on top.
Phoenix