Avoid Evelyn Underhill?
She is about the 20th century’s greatest scholar of Catholic mysticism, precisely because she was a mystic in her own right.
The only reason she couldn’t come into full communion with the Catholic Church was because her Anglican husband was anti-Catholic and prevented her. This extenuating social circumstance notwithstanding, she identified with Catholicism.
Her understanding of Catholic mysticism was second too none.
She wrote in one of her Letters:
Ignoring her because she happened to remain in the Anglican Communion would be a travesty. All the baptized are placed in imperfect communion with Holy Mother Church.
St. Isaac of Nineveh was a Nestorian yet his works are universally revered throughout Christendom because they are theologically orthodox. Evelyn Underhill is in the same boat.