I ended up using both a trackball and a graphics tablet at the same time. I put the trackball in my lap. It does look dorky but I'd rather look dorky than have a permanently sore arm, shoulder and back.
I also try to use the keyboard as much as possible. I prefer to use a key combo to a mouse operation if the option exists, and it usually does.
I went to a chiropracter when the pain was particularly bad (before I got the trackball and tablet). Along with his advice on correct hacker posture, he told me that I had to stop doing any washing up because my height means I am bending at an awkward angle to get down to sink level -- and that he would even write a note to my wife to that effect!!!