I thought the judiciary implementation was left to Congress in the constitution and they made up the size and terms of service for the federal courts.
So no constitutional amendment required.
Size, yes. Congress controls the size.
Terms, no. The constitution sets them for all federal judges as “during good behaviour” which we interpret as “life unless they are impeached and removed”.
You’d need a Constitutional Amendment for terms, as the Constitution currently is a de facto life term.
It is true that Congress could add justices as the number is set by statute. It’s been nine since 1869.
FDR wanted to pack the court, but was shut down. These new communists won’t hesitate to pull the trigger if they ever get power back.