After graduating in Experimental Psychology, in the field of Motor Control, I worked on a research project on keyboard designs which intended to prevent Repetitive Strain Injuries / Work Related Upper Extremity Disorders (arm and shoulder pain).
The study I did was a usability study of a vertical keyboard, the Yogitype keyboard with integrated mouse, for images of this design, see:
Yogitype keyboard (Deutsch)Yogitype keyboard (UK)We found in our study that people could easily learn to type on it, within a few weeks, when practicing for only a few hours per week. The keyboard has the qwerty layout, but the keys are on the back, but you can see the letters and symbols of the keys on the inside you're facing (you must have learned to blind-type using the ten finger system to use the Yogitype).
We also found that ElectroMyoGraphic (EMG, electrical muscular activity) levels in muscles prone to RSI/WRUED (arm and shoulder pain) were lower when using the Yogitype keyboard than when using a conventional (horizontal) keyboard.
I don't know how important it is for you to have a comfortable keyboard; I just noticed on the English website I just linked to that it is very expensive (on the manufacturer's website (the German one I just linked to) I haven't found the price yet) so it might not be useful for you...
I wish you good luck finding a keyboard that is comfortable for you.
The yogitype keyboard costs about 500 pounds (that's more than 750$) I might seem scroogey but I'm not that keen on spending almost a thousand dollars on a keyboard.
It seems to be quite nice, and I can buy it in a bundle with a mouse.