It's advisable for beginners to use whatever shaft fits them.

Steel or graphite is a personal choice. For more athletic players, I like to fit them in steel - the extra weight helps to keep their swing 'simple' (for lack of a better term).

I say try steel in your 3 wood, especially if you think it will help. Now, that said, please know that there are lots of graphite options out there - I'm sure ONE of them will work for you.