hi cashier graham,
i think i have the same problem as you! i've done 10 years of wing chun on and off and want to do something more internal. after a bit of research and dabbling in taiji (which doesnt seem to work for me now i've trained in wc so long..) i came to the conclusion that xingyi is the one.
like you i only have a book: Xing Yi Nei Gong - Miller and Cartmell, got it off amazon.com. Its a great book for the nei gong exercises, and has info on san ti trinity posture too. i recommend it.
I looked for a teacher in my locality too (south wales), Bob10 recommended a guy in Goole which is near Hull, also my friend Mike Hart recommended his sifu who lives in scotland. i can pass on the details if you'd like.
i guess it comes down to what you feel is quality, my best opinion is to travel to see those who can teach you something, i intend to do this when i can get some money together.
i hope your search is fruitful.
fool
Ecce nunc patiemur philosphantem nobis asinum?
what transcends the buddha and the law? Cakes.
"Practice is better than Art, because your practice will suffice without art, while the art means nothing without practice." - Hanko Doebringer, 14th century