Clerics are very, very weak healing wise at level 5. An ancients Paladin can do comparable healing, but has much better damage. At cost of doing aoe healing less often per day.
Either way, make sure to steal hellrider's pride and obtain the amulett that lets you cast mass healing word from the underdark. Omeluum has a ring that slightly improves healing after doing his quest. There's a ring that gives automatic bless on healing. You might already have all of those items.
https://bg3.wiki/wiki/The_Whispering_PromiseThat combination is more important than anything else.
Though... The most literal battle medic is a hasted pure fighter throwing potions like a maniac. Wouldn't recommend despite the hilarity. (Life) clerics come online with warding bond and a very powerful healing spell eventually, but until then, it's tough. War clerics you can fix somewhat by modding the class into being useful, but it's possibly the weakest cleric class in vanilla. Just a fair warning.
If you want damage at a distance, go light cleric. If you want aoe close combat damage, go tempest cleric. If you want single target damage, oath of the ancients. Life clerics are great, but you can't dip into the subclass. You need a lot of levels to get to the good spells. If you're really, absolutely, *only* looking to dip, I recommend going oath of the ancients 7 instead.
The one problem is that this doesn't give you sanctuary (that's on the devotion paladin, who isn't really the healing subclass). Ancients makes up for it a bit by taking half magic damage starting level 7, for themselves and close allies. The lack of sanctuary and spirit guardians (aoe) can still be incredibly painful in Act 2, however, so I'd really just recommend sticking to an actual cleric, light, tempest or life. A Paladin is much less versatile than a (mostly) pure cleric. Your party composition isn't only lacking a healer, but an aoe caster.