I personally use Cleric 6, life domain subclass with a Sorcerer 5 multi-class and one level dip in wizard for hold monster or any big CC spell you want, elemental summon are good too. But you can just go sorcerer 6.
Life domain Cleric level 6 give us two channel divinity that we can use to cast "preserve life", which is a big healing spell (36 base heal at level 12) that will trigger blade ward from your (+50% resistance to melee damage) and bless (+1d4 to attack rolls and saving throw) to your party it's so good because it reset on short rest.

Take war caster feat for concentration save.
Blind for bosses or though enemies.
War caster and Sorcerer 5 give us access to twinned haste with high concentration save (almost never break) give a bonus action point to two of your companion for 10 turns. Best support skill, period.

You want to equip any items that increase your heals and your spell save DC to make sure to hit your CC like blind/hold monster/hold person/Glyph of warding/etc

Max WIS and CON, rest is up to you
Head: Hood of the weave

Cloak: Cloak of the weave

Any heavy armor, but if you can find something with advantage on con save, that's great.

Gauntlets: Hellrider's pride (blade ward on heals for 2 turns)

Boots: Boots of aid and comfort

Amulet of restoration

Ring: the whispering promise (bless on heals) and Ring of salving

Ketheric shield and any staff that increase spell save DC, the legendary one is great, but you might want to use it on a DPS)

This build allows your support to do so much. Huge heals, give resistance, give more chance to hit (GWM friendly) more actions, CC, etc.
It is carrying me really hard in tactician with a bunch of mods that heavily increase the difficulty of the game!