Best personas to get for okumura?

Hi persona 5 is the first persona game I've ever played so I'm not too familiar with powering up personas or creating personas or even buying them. I've been stuck on okumaru for the last couple of days . I rushed through his palace so my whole team is under leveled. (High 30s). I'm playing on merciless difficulty for that extra weakness. If you need more info about my party to help me please let me know and thanks in advance! 🙏