Kana built by stacking Veteran's Endurance, Ancient Memory, items that give bonuses to healing, and eventually using The Dragon Thrashed chant can almost solo the game, and is a strong addition to any party providing healing and damage. Build him tanky as you can and let his passive healing/damage do the work. Probably the best companion for what you describe.
I personally recommend a PC Priest, as Durance is kind of slow for the job. https://forums.obsid...-guide-priests/ This should give you all the information you need.
As for other potential party members, Aloth is strong because Wizard is strong. Once you know what spells to use and how to use them ( https://forums.obsid...her-and-wizard/ ) he should do a ton of work. That said, I didn't have a Wizard in the party I beat the game with, so it's not mandatory.
Grieving Mother is a Cipher, and Cipher gets tons of powerful options.
Hiravias is a druid, and Druid gets tons of powerful options (also he's hilarious).
https://forums.obsid...ns#entry1788267 A Pallegina built based off this had the highest damage in my party. Many times, she'd kill lone enemies before they did anything. I personally rotated pistols, but the core concepts are the same: ranged, Fire-based Pallegina is strong. That said, it benefits greatly from knowing the location of certain gear, so it may not be best depending on what you're doing.
So PC Cleric, Kana, and then pick 1-2. Luckily, only Aloth is available in chapter 1 of the above 4 I recommended, so you'll know how you feel about him by the time you get the others so you can decide how you feel about Wizard.
The people I didn't recommend, like Pallegina, require more knowledge of the game's systems and gear. Only reason I put Pallegina on here was because I enjoyed her so much that it might be worth the effort to look up the location of a few items to make the most of her. Wrath of the Five Suns is extremely powerful and fun in this game, imo.