It may not be financially possible for you to but new furniture when the old stuff seems to be hard and uncomfortable. It is possible, however, to get foam inserts to put in the covers and make things fuller and easier to sit on. No one wants to sit on a chair you can feel the springs or hard wood if it is supposed to be an overstuffed comfy chair. You can either get all new cushions, new foam for the existing cushions or add some more foam to what is already there.
When trying to make a chair more comfortable, do not overlook the seat backs. The cushions in the back part of the chair can be just as worn and uncomfortable as the bottom cushions. There is no need to have a sore back from sitting in a chair that has not support. Replace all the cushions or put in an insert to help keep your back straight. You will be surprised at how much better you feel from something this simple.
One of the big advantages of having a foam mattress is that the foam can be replaced or reinforced without having to buy a whole new bed set. This is no possible with an innerspring matress. If there is any one thing you can do to alleviate back pain, it is probably make sure you are sleeping well. If your bed is comfortable, you will be able to sleep through the night without waking up all night and tossing and turning because you are uncomfortable