A single amendment wouldn’t require a convention. AFAIK, a convention is for a constitutional overhaul. So what would be required at the amendment level would be this issue passed by the proper number of States. In the alternative, it could be passed as a federal law by Congress. However that would presume Congress would want to draw attention to it’s main form of wrongfully imposed power and then limit itself from access to that wrongful process. Needless to say, it’s hard for me to see that happening. So if it ever happens I see it arising from the several States in the form of a constitutional amendment.
Amendments must first be formally proposed. There are two ways to propose amendments - via Congress or via a convention. Since you don't want a convention, that leaves Congress.