+1 on Acoustic Labs (esp. the albums Atmospheres, Glass Harbor and Scenes vol. 1)
+1 on Mazzy Star’s vocalist Hope Sandoval, but her chill-est work I would say is what she did more recently with “The Warm Inventions” - Who are your favorite female vocalists - #29 by abm0
To these I would add Helios (several albums) and Jóhann Jóhannsson’s “Orphée” album as some of the most chill things I know.