“sm29” mentioned Rav Shalom Arush.
His writings are amazing! I highly recommend “S’dot Yaar” an absolutely great and very readable sefer on hitbodedut (personal prayer). It is also now available in English (Forest Fields) translated by Rav Arush’s talmid muvhak the wonderful Rav Lazer Brody.
If everyone would read this sefer and implement what it teaches, NO ONE would ever go “off the derech”!