Hi tigerlily,
The type of materials in a mattress is a preference choice and has very little to do with whether any mattress is a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) or whether you will sleep well on it. There are many variations and designs in every mattress category (latex, memory foam, innersprings etc) and the design of the mattress and how well a specific mattress matches your unique needs and preferences is always more important than the type of materials that are inside it. In other words … the type of material isn’t what makes a mattress suitable for some people and unsuitable for others (outside of their preferences) it’s always the specific design and combination of layers and materials.
While I can’t feel what you feel or see you sleeping on the mattress … I can certainly provide some information that can help you with the detective work that can be involved in finding out the most likely cause of your “symptoms”. There is more about the more common “symptoms” that people can experience on a mattress and some of the most likely reasons for them in post #2 here and the posts it links to.
Post #2 here and post #4 here also has more information about primary or “deep” support and secondary or “surface” support and their relationship to each other and to firmness and pressure relief and the “roles” of different layers in a mattress that may be helpful in clarifying the reasons for your symptoms as well.
If your mattress is too firm … then some of the suggestions in post #2 here may also be helpful.
It’s possible that you may need both firmer support layers (such as the firm in the middle) for better “support” and thicker/softer comfort layers (to help with pressure relief) so there may not be a single change that solves all your “symptoms”. A different pillow may also be helpful with shoulder issues on the firmer combination (S/F/M) as well.
My “best” suggestion though would be a more detailed conversation with SleepEZ who have more experience with “fine tuning” their mattress than anyone else and will be your best source of guidance.
Phoenix