You have taught thousands of people how to strengthen their back and improve posture. The No. 1 cause of back and neck pain is poor posture. I see a lot of upper back and neck discomfort and lower back discomfort, usually from sitting too long at a desk or computer. Nonspecific back pain is pain that can't really be attributed to any specific cause. I believe it usually involves strain and stress of soft tissue like tendons and possibly ligaments.
People spend a lot of money purchasing high-quality beds with special mattresses and box springs.
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 your self in alignment even when you sleep. For instance, side sleepers need to make sure the pillow width is not too low or too high.