Moon Druid would be good, or shepherd. The bard isn’t likely to want to be in melee, the wizard definitely won’t, and it’s important to not rely on one person to tank the world (especially since paladin’s are bursty). A moon Druid can take a ton of pressure off the paladin, and has tons of great spell options that the party otherwise will miss out on.

Or cleric! Clerics apply to almost all situations. Focus on life domain to support bard, giving him leeway to burn slots on non-healing, too. Go war domain to be tanky melee bros with the paladin. If you go cleric, there are also a boatload if really fantastic “thank god we have a cleric” spells: zone of truth, dispel magic, etc.