Alan Davey put me on to the fact that Albert Camus' novel sometimes known in English as The Stranger and sometimes as The Outsider was being commended to Christians by Leland Ryken. See here. It is a book I have long been aware of and so I got hold of a copy (a Penguin paperback) and found it an easy enough read as the book is short, well written and quite gripping. I guess you are supposed to sympathise with the protagonist, which I did not but that did not spoil it. It is quite an old book now (from 1954) and lacks the impact it might have had because such existential thinking has become more common. It is still a though provoking and interesting book and worth a read. I enjoyed it so much I got straight on to The Plague but that's a longer book and I am taking it at a more leisurely pace.
Bonhoeffer uses a similar phrase 'worldly Christianity'. It's J Gresham Machen that I want to line up most closely with. See his Christianity and culture here. Having done commentaries on Proverbs (Heavenly Wisdom) and Song of Songs (Heavenly Love), a matching title for Ecclesiastes would be Heavenly Worldliness. For my stance on worldliness, see 3 posts here.