So originally, I had two shims in (Business cards, folded in three and held together with double sided). So quite a lot of shim. That angled the neck and got the action to an acceptable level, but it meant that at the end of the fretboard (the end at the body that is), the strings were completely bottomed out when I played anything above the 14th fret iirc. So I took one of the two shims out. That made the action higher and the issue with the strings bottoming out is still there, although maybe not quite as bad, but the bass is still effectively unplayable...