Buy Broom Besoms and Young and Souple Was I are different songs. Burns had an apparently incomplete version of "Sair Fyel'd, Hinny," https://babel.hathitrust.org/cgi/pt?id=uc1.c034406758&view=1up&seq=110 which encompasses all but the "beld head" entendre from "Young and Souple," and has an appropriate chorus and much finer last verse that brings the song together. It is in Northumbrian Minstrelsy. The lyric is "Young and Lusty Was I" in Northumberland, and a tune of that title is in the Atkinson MS of 1695. Burns indicated "same tune, same chorus" for "Young and "Souple," but the chorus of "Buy Broom Besoms" does not work with the lyric. No one stands on the street and sings sadly of their E.D. in order to sell broom. "I Maun Hae a Wife" was indeed on MacColl's Songs of Robert Burns, but (as with "Cauld Kail in Aberdeen" on the same LP), Burns never claimed to have written it, and it bears no mark of his style. The Caledonian Museum (1825) has a craggier version of the tune, and Matt Seattle published a third variant, "The Busoms," from an undated Scottish MS in his book O'er the Hills and Far Away in 2006.