I would like to make this recommendation with a small caution. Celtic Women, Peter Berresford Ellis (1995) is a very interesting read on role of Celtic women. However, one doesn't need to get very far into an Ellis text to realize that he is a definite Celtofile. My sense is that this sometimes inspires him to get carried away in his romantic notions of how he thought things should have been.

The good thing about Ellis is that, in addition to being very easy to read, he usually includes a rather ambition bibliography, which makes further research a lot easier. Access to a good university library may be necessary to carry studies to any depth. I've found that most commercial releases on the subject are lacking in real meaty information and rely heavily on the imagination of the author. I know, that's history by definition, I suppose, but I've had a lot more luck finding good, solid information in the basements of scholarly libraries, back in the compact shelving where they hardly ever see any humans.