Fittings are so worthwhile IME and IMO!
Out of curiosity, why did he suggest a compact double? Are you on a triple now and does that, at all, influence why your knees were tracking inward? I ask because mine do the same thing and I know it has a lot to do with q-factor (the width between the pedal spindles). And what pedals are you currently using? I have Look Keos; I wonder if I'd be better off with Speedplays because of spindle length. I've already switched to a compact. Triples cause my right ITB to hurt terribly as a general rule.