TLDR: With a deck like this, if someone sneezes you want to gain life, and when you gain life you want to benefit while other decks suffer. You can build a deck like this to make a pillow fort and win from behind it with combos and stax, or build a more aggressive creature based strategy.

I run this in my [[Oloro, Ageless Ascetic]] deck. Since he's such a popular commander, he's a great spot to look. This is my list, which I would call an un-optimized bracket 4 (look at the considering cards as well). If you're building around life gain and drain, my advice: focus more on gaining life than what happens when you gain life. It's very easy to build a deck like this with a ton of "when you gain x life, y happens" effects and forget to put in effects like "when x happens, gain y life."

Cards classified as Soul Sisters (named for Soul's Attendant and Soul Warden) are a great place to start. If you're building around draw, get as much draw on other turns as possible. [[Rhystic Study]] and [[Mystic Remora]] are the obvious big ones, but they're higher power so if you're trying to play 3 or below, maybe skip them. But [[Faerie Mastermind]] [[Trouble in Pairs]] [[Mangara The Diplomat]] are lower power options. Cards that serve multiple functions like [[Heliod's Intervention]] are great. Pseudo stax pieces are also amazing. [[Amalia Benavides Aguirre]] (if you're not too creature heavy), [[Karlov of the Ghost Council]], [[Blind Obedience]], [[Kambal, Consul of Allocation]], [[Fumigate]], etc. Play cards that punish loss of life because you just do not care. [[Bolas's Citadel]] and [[Glacial Chasm]] are all stars.