You may not know this, but...humans are not meant to sit for long periods of time. Unfortunately, in our increasingly tech-advanced, and motoring world, that is exactly what we do. And now we're paying the price. Or I am, at least. And a major contributor to my current physical issues--improper desk/chair ergonomics.
The chair I've used at my paid job the last five years has arm rests--but they're too wide apart for me to rest my arms on when typing or mousing. The Occupational Therapist who assessed me was, to put it mildly, shocked I had used the same chair for five years w/o support. He explained that the muscles used the most in desk/computer work--located where the arm attaches to the body--are very SMALL and not meant to support the full weight of the arm--arms are approximately 10% of total body weight (divide by two and you have weight of each arm)--for hours on end. He was not surprised I am having pain/numbness/weakness in my arms. Only surprised how long it took to catch up with me. Oy.
So...make sure whatever chair you use SUPPORTS not only your back and head, but your arms when typing/mousing. Shoulders in a neutral position next to your body; elbows at a 90 degree angle and again close to your body (no reaching out or sideways); feet flat on floor; trapezoid muscles (large upper back muscles) down and back (think shoulder blades flat against against ribcage); chin tucked slightly in so head is not canted up or down; monitor centered a tad lower than eye-level so you're looking slightly down at it. Other tips Here. And make sure you get up and stretch REGULARLY.
Occu-Therapist recommends sitting for no more than an hour at a time and then standing for an hour (so a sit/stand desk is a good option) with frequent stretch breaks in between (every half hour was his recommendation). My physiotherapist also recommends daily cardio physical activity that activates all muscles of the body (cross-country skiing/snowshoeing/swimming/etc) -- as she said: your only exercise routine should not consist of desk work. And if you're feeling a twinge, or ache, in your legs/back/neck/arms/shoulders--see a physiotherapist BEFORE it blows in to something serious and long-term.
And now I have to go, because the short time it took me to type this is causing pain/numbness in both arms.
PLEASE...take care of yourself. You can't get a replacement body on Amazon or anywhere else.