A couple from the church were in Florence recently. I was surprised to realise that the above picture which I recognised as a Cranach portrait of Martin and Katie is housed in the Uffizi there. Not sure how that happened.
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.