According to some reports Justice Breyer will be retiring at the close of this term or once his successor is elected. It is possible that the Supreme Court will add four members over the course of the six-year period. Justice Gorsuch was confirmed by Kavanaugh on April 17, 2018, Barrett on October 2018 and Breyer as the replacement for Justice Gorsuch in 2022.
The Supreme Court had a very rapid turnover during the Nixon era. The 1969 confirmation of Chief Justice Burger and Justice Blackmun was in 1970. In 1971, Powell/Rehnquist became permanent.
FDR, however, set the current-day record. Roosevelt had nine appointments between 1937-43: Black Reed, Frankfurter and Murphy; Stone, Byrnes and Jackson. However, the OG GW holds the ultimate record. In 1789, President Washington appointed five justices and added six during his remaining tenure.
Remember that Justice Breyer served as the junior justice in July 1994 through January 2006. A court that has such stability may not be seen again. Justice Barrett served as the junior justice during approximately two terms. Soon someone else will be required to take the responsibility for answering the door.