Embody + Aeron and alternate between them. Always amazes me people will spend incredible amounts on a car, but will skimp on something they spend 8+ hours a day sitting in.
+1 for alternation. I rotate between an Embody (when I want to lean back a little), a flat wooden chair (when I want to sit up straight and not support my back against anything), and a wobble stool (when I want a bit of forward tilt). The Embody is perfectly comfortable on its own but I tend to start to veg out mentally if I'm leaning back all the time.