In case you're still interested in suggestions, you might try concentrating on playing melodies for awhile. This is something I've practiced a lot in the last couple of years and I think my playing has improved as a result. It's much easier to relax your hand if you're not playing chords. You could throw in some chords, too, if you like, perhaps higher voicings on just three or four strings.

The wide neck of a classical guitar takes some getting used to, but I think it's worth it. On the rare occasions that I get to play a steel-string or an electric guitar, I find I have to get used to having less room to manouver with my right hand.

I never fret with my thumb and have medium-sized hands. I don't think there's anything wrong with this technique, if one is happy with it. I avoid playing anything that feels uncomfortable. There's no reason ever to do so.