Nothing is worse than a bad mattress. I know that from experience. Your back hurts, you are not getting a good night's rest, and this can effect every facet of your life. I always like staying in hotels, because their beds seem to be so much softer and nicer than the one at have a home (aff)!
Once of the easiest things you can do is shop for a new mattress. The cheapest thing to do is get a mattress topper. This will make your mattress more comfortable. However, if you need a new mattress, sites like Memory Foam Express have a lot of choices for you. They have everything from budget mattresses to memory foam mattresses (which are my personal favorites!) They also have mattresses for whatever size bed you may have (I never realized mattresses could be so many different sizes!). I'd definitely be surprised if you didn't find a mattress that would fit your needs!