They have the same options as everyone else in the federal government — no more, no less. All federal employees can access health care insurance through the Federal Employees Health Benefits Program. That includes Supreme Court justices, members of the Senate, congressional aides and the janitorial staff in the Department of Health and Human Services.
(Though the Supreme Court declined to provide specifics on the health plans of the individual justices or how many of them even participate in the Federal Employees Health Benefits Program. Some federal employees elect to receive their coverage elsewhere — through a spouse’s plan, for instance.)