Glad that you enjoyed Peggy Lee's Capitol transcription recordings. Next, try her McGregor transcriptions, which are from around the same period -- January 1945, to be exact. (The Capitol batch was recorded between 1946 and 1949.) It is actually a fairly small bunch -- less than 20. Almost all of them are found in the following CD:
Note that one of the songs which you mentioned [“Someday Sweetheart”] is also heard here -- in a different, slightly earlier version. The accompaniment is the same quartet featured in the recordings that you favor, augmented in this instance to a septet through the addition of clarinet, sax, and trumpet (Billy May's).
Caveats: you will be getting a budget production -- no liner notes, nor much in the way of discographical information. More crucially, the sound quality of this release (also available on cassette tape) is not of the same high caliber as that of the Mosaic boxed set. All the selections are in need of slight speed correction. The track runs faster than it should, and Peggy’s voice sounds a bit more girlish than usual, though very pleasant all the same. Despite such shortcomings, the entire CD makes for very pleasant listening. (If we leave aside the need for pitch correction, the sound is fine -- crystal clear -- and the playing quite jazzy. Besides, no better version of that material has shown up on the digital market as of yet.) Inexpensive CD copies can be found with relative ease.
Ivan