I've just ordered a Logitech Trackman Wheel. I'll let you all know how I go with that when I've used it a week or so. The one thing I like about my mouse is the wheel and the ability to zoom in and out holding Alt and scrolling the wheel up or down.
I don't regret buying the tablet, but it's certainly not for Indesign work as a rule. Invaluable for Photoshop functions.
I recently purchased a compact keyboard with no numpad (thought it exists with the use of the Num Lock function key on) to try and reduce the amount I stretch. It's not bad at all. The Back Space key is smaller and some of the keys like Ins and Del are at the bottom so this all needs getting used to, but like moving from a manual car to an automatic or vice versa, it's all possible.
It's only 30cm wide, so the new trackball and tablet should fit quite comfortably at a combined width of around 65cm, and not having to move the mouse to bring in the tablet.
I've also got a wrist rest on order.
Any other thoughts of improving one's comfort and well-being certainly welcomed.