As I've said before and will say again: A lot of the secret to ergonomics is to experiment with very small, ad hoc changes in your environment. I cured a major chronic pain in my right arm by raising my mouse three inches. Get a selection of books for putting under your monitor for changing its height. (Or invest in those awesome Ergotron arms -- they are great.) Also: A keyboard tray with fully-adjustable articulating arms is your friend.
That's where I put my old XML/XSLT books.
I wonder if today's physics students use books like that anymore, or if it's all gone Mathematica and Google. I would bet on the latter, but I can't be sure. It's been a long time since I looked up an integral.
And both are many, many times more comfortable than anything else I've used.
I suggest finding a showroom and trying it out. Herman-Miller has plenty of resellers in major cities.
If you're the sort of person who puts things in their backpockets - DON'T! Even a thin wallet twists your butt enough that it ends up causing backstrain.
I sit in one 8+ hrs a day and I don't know if it doesn't fit me correctly (I'm 6'4") or what, but I'd prefer a different chair. Unfortunately the only other chair available to me is some terrible ikea chair that is wrong in ever possible way.
For as much as they cost, I thought they'd be way more comfortable.