Voices are my forte. As you pointed out, the most important thing is to find voices that do not hurt to do; if you are in any kind of physical pain after doing a voice you are doing something bad to your throat and you should stop doing that voice.
The parts of our body that make our voice range from in the middle of our skull all the way down to our diaphragms. You can pitch your voice from any point along this trail. Putting your voice at your diaphragm makes it deeper, putting it in the top of your body can make it higher. So, for female voices, allow your voice to resonate from anywhere around the top of your throat or the back of your mouth.
For a simple female voice, follow these steps: Go into a whisper (a true whisper does not use the vocal chords), and then add in a very soft, low-volume voice from the top of your throat. Make sure to maintain the breathy quality of the whisper. Avoid falsetto - women do not talk like Monty Python Old Ladies.
Pay attention to how people speak: women have very different vocal rhythms than men. An easy rule to remember: Men make statements, women ask questions. It sounds awful, but it's true. If you raise your voice at the end of any sentence it will sound more feminine.
And finally, it's hard to hit on any voice in the abstract. Listen to audio of women with distinctive voices, and try your best to copy them. I don't expect you to become a skilled impressionist, but it will help you make vocal discoveries.