JAZZ Sarah Vaughan. ''Crazy and Mixed Up.'' Vaughan, vocals; Roland Hanna, piano; Harold Jones, drums; Andy Simpkins, bass. Pablo Toady. 2312-137. Can there ever be too many Sarah Vaughan albums? Or enough, for that matter? Not if they're like this latest one, which is a pure joy. At last Sarah is backed up by musicians of her own choice. Why can't she always have this caliber of band on record and especially in concert? The songs she has chosen are excellent. Along with old chestnuts like ''That's All,'' ''You Are Too Beautiful,'' and ''I Didn't Know What Time It Was,'' she has included three lesser-known but lovely songs: Raymond Scott's ''Love Dance,'' David Rose's ''The Island,'' and Roland Hanna's ''Seasons.'' Everything on this set reflects Sarah's impeccable taste, from her lightly swinging arrangement of ''That's All,'' to her upbeat scat rendition of ''Autumn Leaves.'' Her voice, although a bit flat on top at times, is as full-bodied and rich as ever. No wonder this album is so good - Sarah produced it herself.