Hi pressurepts,
What type of mattress do you have (make and model?)
It may be a good idea as well to talk with the retailer or manufacturer to find out more details about your mattress or to ask for suggestions as they may be more familiar with your mattress (or have helped other customers with a similar body type and symptoms)
Primary support comes mainly from the deeper layers of the mattress so the latex on top wouldn’t be affecting this so much. Secondary support comes from the upper layers which are meant to provide both pressure relief (allow the more pointy parts of the body to sink in enough) and to fill in the recessed gaps in the body profile. I would also keep in mind that your “comfort layer” is really a “comfort zone” and may not just be the thickness of the top layer (see post #2 here)
This is certainly a possibility. It could very well be that your comfort layer isn’t thick enough to “allow” your shoulders to sink in enough before they are “stopped” by firmer layers. Neck issues can also come from twisting of the head and neck or sleeping positions where the upper body or spine is twisted. Part of this could be your body trying to “twist away” from pressure points on your side.
Besides the ideas in the mattresses section of the site … post #2 here along with post #3 here and post #6 here and post #6 here are all examples of posts that may be helpful in helping you to “diagnose” what may be happening and what may work best to correct it.
My “guess” would be the thickness of your comfort layer but without being able to see you in person and to know more about what is in your mattress and your body type and other relevant information the best I can do based on “theory at a distance” would be a be a guess
Phoenix