"What's the best mattress that I should be sleeping on? What's the best mattress for me?" While in general we tend to say that a firmer mattress tends to be better for a lot of people, the real answer is that everyone is going to have a better mattress for them - everyone has the best mattress for that person.
There's no substitute for going to a store and trying out mattresses and seeing which one is the most comfortable for you. There is no real right or wrong answer here, except that you want to be sleeping on a newer mattress. You know — if the mattress is really old and not supporting you, that's not good. But, otherwise, the best thing to do is to go to the store and try out a bunch of mattresses and see which mattress is best for you.