I also love i3wm but there are a few tiling window managers available on macOS [0] [1]. Not as easy to use as i3 last time I tried them however that was a while ago and they definitely deserve another shot.
I really like jigish's Slate[1] for this (maybe I'm just too lazy to switch) but sadly it's not being maintained, and I just noticed that neither is mattr-'s fork[2] as of this month.
[1] https://github.com/jigish/slate [2] https://github.com/mattr-/slate