Alexander technique done right will improve a lot more for you than your piano technique... get your back straight, stop you slouching, breathe better, and in general terms being a lot more aware of your body and your posture. If you sing, it'll improve your sound greatly, and even things like sitting at your desk at work will improve.
One of the common starter exercises is imagining you've got a helium balloon on a string attached to the top of your head, and it's holding you up - and if you keep that image in mind, whatever you're doing at the time, you'll find your back and neck should come into line... some of the concepts are a bit abstract but once you get them and start using them day to day your back especially will thank you for it!