https://youtube.com/playlist?list=PLGMYnukvmgiXXFxuTKDvZfw-e...
I listen to it while I work.
Sunset Mission by Bohren & Der Club of Gore is very very sleepy Jazz (they have released more albums, but this one is my favorite by a wide margin)
Long Ambients 1 & 2 by Moby - he was kind enough to make them available for download free of charge, too
Under Wires and Search Lights by Marconi Union
In A Silent Way by Miles Davis
Pretty much anything by Sigur Rós. It's not strictly speaking instrumental, but the lyrics are Icelandic, which I don't speak, so it's close enough
Cocteau Twins recorded many very ambient-ish albums. Not instrumental, but the "lyrics" are mostly glossolalia, so not distracting (at least for me).
In fact, the use of loops described in this article reminded me of what Reich called "phases", basically the same concept of emerging/shifting melodic patterns between different samples.
Actually, check out the whole Ultimae catalogue: https://bandcamp.com/ultimae
some of the artists below are not strictly speaking ambient as in brian eno kind of ambient
jogging house, r beny, biosphere, anthony childs (surgeon doing ambient), abul mogard, alessandro cortini, alva noto (glitchy ambient), benoit piouliard, bing & ruth, bvdub, mu tate, jake muir, ulla, log et3rnal, space afrika, heurco s, donato dozzy - plays bee mask, imaginary softwoods, jo johnson, koen holtkamp, mountains, kyle bobby dunn, oneohtrix point never, neel, pendant, romeo poirier, domenique dumont, …