I prefer my own, but am ready to introduce both of them:
Introducing, firstly, an amendment that Section 3 be amended to read
(...) and Class B, which shall comprise Senators elected by a form of proportional representation.Secondly, (irrespective of how the first vote goes) an amendment that Section 3 be amended to read "...Class B, which shall comprise Senators elected via proportional representation by means of single transferable vote."
Thirdly, and only if both previous amendments fail, an amendment (which may be recognized as a friendly amendment) that Section 3 be amended to read
...Class B, which shall be elected as the Senate shall specify in appropriate legislation."