The number is nine. Period. Due to the random nature of death, some Presidents will get more opportunities than others. Increasing the number of justices won’t change that. All need be done is to be sure that those selected are demonstrably impartial and will in a carefully reasoned way apply the law. The problem isn’t really with the Supreme Court. It’s with Congress. They have passed on the tough decisions (civil rights leaps to mind). Let’s get them to do their jobs.