The phrase "advocated a single" is correct and usable in written English.
It can be used when discussing support for a specific idea, policy, or approach, often in a political or social context.
Example: "The committee advocated a single approach to address climate change effectively."
Alternatives: "supported a unified" or "promoted a singular".
Ms. Magie was an ardent follower of Henry George, who advocated a single tax on land.
The Republican state chairman, George M. Sundheim III, long advocated a single Republican on the ballot, but gave up on the idea as it became apparent that there was no consensus candidate.
After Oslo he argued that separate Palestinian and Jewish states would always be unworkable and, although he recognized that emotions on both sides were against it, he advocated a single binational state.
She confessed to Thomas Fulbright that, "The reason I started writing some of my own stories was because I wanted to portray the self-reliant, self-supporting woman". Petrova wrote, for example, the scenario for More Truth Than Poetry (1917), which advocated a single sexual standard for men and women.
He advocated a single rate of income tax - an idea in vogue among some right-wingers today - but also argued for supertax on inheritance to prevent the passing down between generations of "enormous fortunes which no one needs for any personal purpose but ostentation or improper power".
Trump in the past has advocated a single government health plan for all Americans, akin to systems in Canada and Britain.
Some advocated a single-payer system — a k a Medicare for all — but this was dismissed as politically infeasible.
He once advocated a single-payer system, but has since said that would make sense only if starting from scratch; now, he vows to work within the current system of employer-based health care.
I've advocated a single-payer universal plan, myself, but that's not going to happen, and no system would be without flaws.
Others are advocating a single international art-crime tribunal.
Some conservatives go further, advocating a single "flat" tax bracket above a basic personal exemption.
