hmm, that's an interesting question. On one hand, hematite is useful because of it's reflective properties, and snowflake obsidion is rumored to work because it has the mirror attribute (the astral) and the blake flecks in it (the earth) tieing the two together. on the other hand I'd point out that crystals seem to be "heavy" they are very earthy and can be grounding...not exactly good attributes if you are trying to leave your body, which requires a 'light' spirit. first off my simple advice is to point out that you are not your body, it is a shell for the you that is inside. your essence, your soul, your spirirt, whatever you call it, that is what you want to move. try thinking about it like that to start with.
Astral travel is also a shamanistic experience. You might try some methods for entering a trance state - this is not exactly astral projection ( well, not necessarily, in certain trances one might find oneself travelling ), but this may help you to experience the feeling of leaving the body. Search for music that seems to lift your spirit in a gentle, ethereal way - this is different music to different people; have to find that yourself. Mediaeval Baebes works for me. Also, meditate on the idea that, to some cultures, the body resides within the soul rather than the other way around. Your spirit can exist on many planes your body, only one. Perhaps by meditating on that subject you may feel less bound to your flesh and bones. If you are a musician, even if you only bang a drum on occasion, you probably enter trance states all the time. If so, draw on that experience as well.