Anything of the pastoral writings by Romano Guardini.
His book “The Lord” is a classic that has a profound chapter on detachment.
His book “the virtues” etc…
St John of the Cross is all about detachment. “Dark Night” and “Living Flame”. Although, they can be deep to the point of distraction, depending on your personal disposition.
St Maximillian Kolbe’s story (I forget the title). The hardships he embraced…