Hi radams,
I would make sure you’ve read post #15 here and the other posts it links to before going in the direction of a complete DIY construction. If you decide that the learning experience is worth the risk … then it would be reasonable to “expect” that you will make a few errors and unless there is a good return policy for the layers you buy that you may end up purchasing some extra layers.
Your design would be “in the range” that would be suitable for you and the criteria you mentioned but there are so many variables and unknowns involved that only your own testing or experience can really know whether the design would work well for you (see mattress firmness/comfort levels in post #2 here). If you have a good reference point and have tested a mattress that is very close to the design that you are considering (same type of latex, same ILD’s, same layer thicknesses, and similar cover) and it was a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) or have at least tested a mattress that was “close enough” that you were confident that the design you are considering would be “different in the right direction” and would be a good match then your odds of success would be much higher.
Without this then you will be using your “best guess” for your original baseline design and then you could make any necessary changes to it using your actual sleeping experience as a reference point.
Phoenix