Is a firm mattress better for people with a bad back?

Not necessarily. We hate to get technical, but firmness isn’t really the issue. What everyone needs is a bed that’s supportive. The feel of a mattress—whether firm, medium, or soft—is a matter of preference (and pressure relief). Ideally, you should be comfortable and supported, whether you’re on your side, back or stomach. If you’re not comfortable and supported, it’s time for a new mattress. A good rule of thumb: whether you’re standing or lying down, your posture should be the same.