The Ella Fitzgerald Songbooks were originally released as box sets (the first three cds or so were the lp release)--and hailed at the time as defining both Fitzgerald's career & the canon of American song. I don't much care for Riddle's arrangements, so haven't spent much time with her songbooks except for the collaboration with Ellington.
By the way, Lee Wiley started doing composer songbook albums back in 1939--I think they were released as sets of four 78s. She is well worth hearing, though more of her songs remained obscure.
If you want more musical variety, in the '90s Verve tended to release a lot of single disc composer-centered songbook compilations--ie, for Johnny Mercer there's one called Trav'lin' Light, another called Blues In The Night & a third (that is just instrumentals!) called Too Marvelous For Words. Great stuff in there, but it is pretty much all '50s mainstream recordings.
The Smithsonian has a series of thoroughly researched single composer discs called The American Songbook Series that compiles from a wider set of labels over a longer period of time but tends to be a bit less jazzy-- https://www.discogs.com/label/637024-American-Songbook-Series