There's been debate about changing the size of the supreme court for a long time. The problem is that if one party does it, the next one can do the same to stack in their favor. That said, just 9 members that are permanent installed with no oversight makes them arguably the most powerful body in the nation. Just one crooked member can be devastating.
I don't have a perfect solution, but I'd start with something more like 21 members, strict oversight into their finances, a third party that mandates recusal, and a shelf life.
The damage of these 6-3 decisions could last decades or worse. They certainly don't represent the people that are much closer to 50/50 conservative/liberal than 2/3 extremely conservative.