Hmm... seems my options are plenty!
Agree with Birdy that the lightness of touch on a keyboard is very important, especially when I'm typing on it for hours a day (no wonder it's worn out!). I'll have a look at the wireless ones, but space is very limited, so I think I'll wear this one down completely, and then look at getting a replacement keyboard. Dunno how easy they are to fit, but it should be a simple clip 'n' screw job
Thanks for all your help and suggestions!