One of the tracks still sounds like you're hearing someone drowning over the course of 17 minutes and it's terrifying. It's the first track here, though I believe they are named / ordered incorrectly. Just comparing 2 minutes in vs 15 minutes.. it still creeps me out.
I'd add Windy & Carl, A Winged Victory for the Sullen, Yui Odonera (lots from the Serein label actually), Max Richter, and most of all Stars of the Lid.
The Orb
KLF (Chill Out)
Tipper
Irresistible Force / Mixmaster Morris
Future Sound of London
Higher Intelligence Agency
Sun Electric
Vermont
Erased Tapes (label)
Apollo (label)
Armadillo (label)
12K (label)
Pop Ambient (series)
Some (perhaps) less-known: Masayoshi Fujita, Yutaka Hirose, Void
Plus 10k+ electronic music artists that dabble in ambient / chill out.
Self-plug: I DJ 2-3x month for Sunday Sundowns with The Ambient Mafia
Ryuichi Sakamoto (Async LP, collabs with Alva Noto)
Kelly Moran
Burial (1st half of Tunes 2011-2019 LP)
Oneohtrix Point Never (Returnal, R plus 7 LPs)
Kara Lis-Coverdale
Harold Budd
Huerco S (For Those Of You.. LP)
Steve Hauschildt
GAS
Laurel Halo (Raw Silk Uncut Wood LP)
Malibu
Loscil
Hiroshi Yoshimura
Kareem Lofty
Ulla Straus
Sky H1
Johnny Jewel
Roedelius (Einfluss LP)
Dedekind kut