May I suggest Evangeline Walton's excellent series based on the Mabinogion, the Welsh national epic - Prince of Annwn, The Island of the Mighty, The Children of Llyr, and The Song of Rhiannon, all from the late 60's or early 70's.

Or The Forgotten Beasts of Eld, by Patricia A. McKillip, from the same period.

Another good choice would be The Dreamstone and The Tree of Swords and Jewels, by C. J. Cherryh.

I hope you can still find them - it's possible they're all out of print.