Hi USSS1865,
Before spending money on switching out mattress layers or buying zoned latex layer, try changing your pillow first. Most of the time, when people have pain from the middle back up to the neck, the real issue is their pillow.
I have often opined that a pillow is like a mini mattress for your head, neck, and shoulders. It helps keep your whole body aligned while you sleep, and offers support and comfort, with a nice cover on it. If your pillow is too soft, like those squishy poly-fill ones, it may not give you enough support. Look for something with more structure.
Shredded latex or latex and memory foam blends can work well, especially if you can add or remove the filling to adjust the height. A little overstuffed tends to work better, as they can flatten a bit, depending on how much fill is in a particular size pillow, ie 5lbs of latex in a standard pillow vs a queen pillow. I have found it is better when the pieces inside are cut evenly, like small cubes or “noodles,” because they give more consistent support than randomly cut/shredded chunks.
If you prefer a solid (not shredded) pillow, go for one with a bit more height and firmness, especially if you sleep on your side or have broad shoulders. Solid latex pillows with a medium to medium-firm feel usually match well with a similar feel mattress. The Oxygen Pillow is a unique option in this category, I cant stop saying enough good things about mine, and the fit of mine. The Malouf Dough pillow is another one to consider. It is slightly firmer than most solid latex pillows, but skip the ActiveDough version because it is too soft. I will break my random cut chunks rule, with the Brooklyn Bedding Shredded Foam pillow. It is a combination of latex and memory foam, but they do an excellent job of stuffing a generous amount of fill, and will send you another bag of fill if needed.
Also, since it has been a year, check your bed foundation or slats for any sagging or bending. Have someone watch you, or record a video with your phone (from the underside of the bed), while you get into bed and have settled in after 10-15 minutes. Then look underneath to see if anything shifts, bows, or flexes.
Hopefully this will help you find the right solution.
Maverick