Not sitting for long beats memorising a perfect posture. What you can actually change at a desk.
Posture advice usually means sitting up straight, but any position becomes uncomfortable after an hour without change. Bodies dislike being loaded in one direction for long stretches. Changing position or standing up every thirty to forty minutes is far more reliable than hunting for a perfect posture.
A laptop flat on a desk sits low, so your head tilts forward naturally. Raising it so the top of the screen is near eye level and using a separate keyboard changes neck position considerably. If you have no stand, a stack of books works.
Feet and back matter more than price. Your soles should reach the floor so the backs of your thighs are not compressed; if they do not, a footrest helps. The backrest should support the inward curve of your lower back, and a rolled towel does the job if it does not. Keep elbows near a right angle so your shoulders do not ride up.
A head is heavy. Balanced on top of the neck, its weight passes straight down; tilted forward, it acts like a lever and multiplies the load the neck carries. Looking down at a phone is the clearest example, and repeated for hours a day it leaves the neck and shoulders stiff. Simply raising the phone toward eye level makes a difference.
Numbness or weakness in an arm or hand, or pain that wakes you at night, can be a different problem from tight muscles. If stretching and posture changes make no difference over several days, or things get worse, get it looked at rather than deciding for yourself.
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