If your LBS is a specialized dealer they will be able to measure your sit bones with a memory foam gizmo. If not, I seem to recall a couple of threads with detailed instructions on how to do it at home.

Just remember that one woman's dream saddle is another's instrument of torture. My cycling buddy is seriously in love with her Selle Italialia lady gel flow. I tried it and was close to tears by the end of a 10 mile ride. I have Specialized Jett saddles on three bikes in 155 width and they just disappear when I ride - don't even think about the saddle.

My LBS has loan saddles that you can try before you buy - perhaps yours does too. It's certainly worth persevering until you get the one that works for you.