You want your spirit to be simple so you practice Zen Buddhism. Zen is all about meditating and letting earthly things go. There's nothing more simple for your spirit than being Zen.
The reading for this kanji is Zen (ぜん), just like the Zen in Zen Buddhism. Pretty easy to remember, no? Just remember that the reading is the same as the meaning. It’s easy!
Currently there are no similar looking kanji which exist in the WaniKani learning system