Might also try Zero 7. Their earlier albums feature vocals from Sia and Sophie Barker, as well as José González. All three have smooth evocative voices.

Sia: Destiny, This Fine Social Scene, The Pageant of the Bizarre, Speed Dial No. 2

Sophie Barker: Spinning, Passing By, In the Waiting Line, In Time

José González: Futures, Left Behind, Today, Crosses

These were all among my favorite songs almost two decades ago, when Trip Hop was at its height. Some I would still consider to be pinnacles of music.