Printable copies of the music and propers for various Masses have been made available here; they were originally developed for John Fisher House, the Cambridge Chaplaincy. They include some interesting features, such as the Offertory Verses. These verses, to which the Offertory Antiphon (or part of it) acts as a refrain, are theologically rich and musically and poetically very interesting. The Schola Abelis in Oxford frequently sings them; they are sung by a cantor, and at the end of verses the full schola repeats all or part of the antiphon. They are not for the faint-hearted, however, as they are difficult. They are optional in the Extraordinary Form, under the Instruction Musica Sacra of 1958, 27 (b) (and de facto earlier too I would assume, hence a 1935 edition of the verses, which are clearly intended for liturgical use). They are not in the Missal, so there is no obligation to sing them, but as it is permissible (and there is usually time) to sing extra things at the Offertory, nothing more appropriate can be imagined than the original verses which go with the Offertory Antiphon in the medieval manuscripts. An edition of the music for these verses, the one produced originally in 1935, is available on the Catholic Music Association of America site here (big pdf). You can also buy a 'Offertoriale Triplex' with the neumes from the oldest available manuscripts included; a putative restoration of the chants with a modern interpretation of the neumes is available for some of them here.
Offertory Confirma hoc, for Pentecost, with the ancient verses, sung by the Schola Abelis.
Those choirs which sing these Offertory verses may well want to provide the congregation with the text, and a translation, which is provided in these sheets.