Having a poor-quality, worn-out mattress can affect you in more ways than you think. Not only can an old mattress be uncomfortable to lie on, but it can also make it hard for you to sleep and can cause back pain, shoulder pain, neck pain and all sorts of other issues. If you have existing chronic pain, a poor-quality mattress can only make it worse. Even if you've never dealt with chronic pain, you might find that you will start feeling sore and uncomfortable if you keep sleeping on the wrong...