Hi miamaelia.
Welcome to our mattress forum! 
A suitable pillow is an essential part of good alignment for the head and neck and upper body because the gap between the head and the mattress and the curve of the cervical spine needs to be supported just like all other parts of the spine. Like mattresses … there are certain “needs” that depend on body type and sleeping positions but with pillows, personal preferences play a more important role because the face is much more sensitive to textures, temperature, smells, and other more subjective “feel” based properties of a pillow. There is more about choosing pillows in the pillow thread here and the other topics and sources of information that it links to that may be helpful.
In general terms … side sleepers need firmer/thicker pillows to prevent the head from sinking too much which can cause misalignment and soreness in the neck and upper body area. Back sleepers need a slightly softer/thinner pillow that will support the cervical/neck area. Stomach sleepers do best with a very thin/soft pillow or no pillow at all. The type of mattress you sleep on and how deeply you sink into the comfort layers will also play a role in the type of pillow that is best. The deeper you sink into a mattress … the “thinner” a pillow you will typically need.
Unfortunately choosing a pillow is like choosing a mattress and there are too many unknowns, variables, and personal preferences involved in choosing a pillow to make specific suggestions or recommendations for someone else. There is no single pillow that is “best” for any particular situation or “symptom” because the goal of a pillow is to keep your head and neck in good alignment in all your sleeping positions and which pillow does this for any particular person or on any particular mattress will vary widely from person to person. In other words, … a pillow that works well for one person with upper back, shoulder, or neck issues may not be suitable at all for someone else with similar issues.
Pillows are also a very personal choice and different people will have very different pillow preferences or different opinions about what they perceive as firm and soft or the general type of pillow that “feels” good to them but some of the information in the pillow topic mentioned above and the posts it links to can help you choose a pillow that is the best “match” for you and the mattress you are sleeping on.
You may want to look into a pillow that has adjustable fill like the Pure Performance LaNoodle Latex Pillow custom-fill with zipper that can be fine-tuned to provide the right amount of support. This is manufactured by one of our Trusted members of our site which means that I think very highly of them and that I believe that they compete well with best in the industry in terms of their quality, value, service, knowledge, and transparency.
I hope you have some time to peruse the information I provided, find something suitable, and return to share your experience on our mattress forum
Phoenix