Pick up First Take by Roberta Flack. There's a killer version of "Compared to What" on there, "Tryin' Times," and of course, the incomparable "First Time Ever I Saw Your Face."
And for that matter, Roberta's second album, Chapter Two, is equally amazing.
By the way, in case you strictly associate Roberta Flack with "Killing Me Softly," these records will suprise you. There's some serious groovin', and they definitely have that sound you're looking for, IMO.
Not so much vocally, but if you like Jazz look for ANYTHING by Lee Morgan.... virtually his whole catalog is available again in vinyl! My first pick would be his 1965 release "Cornbread'.