Well, first of all, there are no pure healers nowadays. (I'd need someone who plays softcore to confirm that, but it doesn't change the fact that pure healers aren't a good way to go anyway).
If you ask, I can answer you, that best healer is of course guardian due to heal abilities. So all you need is club (best would be int or hm + ee), then heavy armor with the same stats (can be also ee, so you can be a tank also) and some lovely charm with stats like str, hm, int, etc + heal charm on your acc slot. (If you don't have good enough charm for your main slot, then you can use heal charm in your main slot).
There are some special occasion that pure healer might be needed, like Mirror Maze run and best option is also guardian, but if you think about normal climb, then better follow your luck, and if you are paladin, go for healback, tanking, etc, if you are monk/ninja just be melee or hybrid (with healback).
Lmk what else would you like to know.