"Is it traditional? What traditional versions are based on it? "

There's a north-east Scottish version in Albert Friedman's Penguin Book of Folk Ballads of the English-Speaking World that includes all the stanzas of the Ramsay version (with fairly minor differences), but also has 1) his request for and her refusal of a kiss; 2) the gifts episode (his gold watch, his prayer book, and a napkin full of his heart's blood) before she leaves him and hears the bells; and then, 3) three stanzas of dialogue between Bawbie and her father, her brother, and her sisters, in which each tells her to take Sir John Graeme and she has to admit that it's too late ("ye know his coffin's makin", "his grave-claes is a-makin", "my heart it is a-brakin"), leading up to the final "O mother dear, o mak my bed" stanza. Friedman reproduces it from Gavin Greig's Last Leaves of Traditional Ballads, 1925, so there may be other similar texts there, or in the Greig-Duncan Folk Song Collection volumes, but I don't have access to these just now to check.