Understand completely,
In that case you might want to try one of these: (ARGH! link blocked... Google evoluent)
Though as Dilbert said, try a few different ones and see what suits you best.
As for your keyboard, your physio should be able to tell you how to sit and have your arms.
Also, these are a good idea: (link blocked... If you google for some carpal tunnel stretches you'll find some)
Doing these stretches and exercises really do help.
On the Cortisone injection front, this CAN help but it varies, I've seen people who've been fine for a year or two after these and also people who it hasn't helped at all.