Also, don't sit for hours at a time. Every hour or so, get up and move around. Also, use a copy holder to keep your work at eye level. Poor posture places abnormal and uneven pressure on muscles, disks, soft tissue. If your upper back is too curved or lower back sags forward, or your head doesn't sit directly over your shoulders, then the curves of the spine are exaggerated, which places uneven stresses and strains, mostly on muscles but eventually on joints.
People spend a lot of money purchasing high-quality beds with special mattresses and box springs.
Yes, the position you sleep in makes a huge difference in how your back feels when you wake up. So whether you prefer medium firm mattresses or concrete hard, it is total personal preference. What is important is that you always keep your head aligned with your spine. You can strategically place pillows to keep yourself in alignment even when you sleep. For instance, side sleepers need to make sure the pillow width is not too low or too high.