Meditation has been life-changing for me, and combines nicely with a good diet and regular exercise to keep me feeling terrific. Negativity and stress are almost non-existent for me, and at 48 years old I have never felt better in my life.
++ for Yoga. You might also try Tai Chi.
I have found the physical demands of Tai Chi to be less extreme than Yoga. I have been in too many car accidents.