One of the delights of being with the Drions was that Donna kindly gave me a set of her beautifully illustrated Day One books for children. They came out a few years ago. I didn't really take them in as my boys are beyond this age group but they are really lovely books They can be found here at the publishers website. See here.
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.