These changes could be made in the current system. A series of witnesses spoke specifically about the electoral system. As I teach my students, the electoral system is not considered purely in the abstract and cannot be taken on its own. It is part of a much larger ecosystem that includes the process of forming the government and the relationship between the executive and the legislature.
Given my area of expertise, my particular contribution deals with the consequences and how to stabilize the situation, should the electoral system we end up choosing lead to minority or majority governments more often than before. I have kept to my field of expertise.
Your colleague asked you whether a referendum is a constitutional requirement. According to constitutional law and in light of the secession reference, I highly doubt it. This reference states that policy initiatives or constitutional amendments are the government's purview, and that the government is not bound by a referendum decision.
Is there a constitutional convention requiring a referendum? I doubt it, since there are three components to a constitutional convention: a practice, a purpose, and the actors' recognition that they are bound by this practice.