'mere sadness' is correct and usable in written English.
It is typically used to describe a feeling of deep disappointment or sorrow that is not serious or extreme, but still has a significant emotional impact. For example, "John felt a mere sadness when he heard his mother had passed away."
It goes beyond mere sadness, and into guilt, and panic.
Instead of inspiring protests, her displays seemed to engender mere sadness and pathos.
His bottom line is that depression is worse than mere sadness or being in a "bad mood".
The computer textual analysis could identify "affect-laden" articles like "Redefining Depression as Mere Sadness" or "When All Else Fails, Blaming the Patient Often Comes Next".
What's more, depression will last for more than two weeks; mere sadness goes away sooner and is often only in certain environments.
In Janet Burroway's latest novel, "the fundamental news has to do with pain, fear, sadness, or the mere and lucky lack thereof".
A Cannes native now based in Los Angeles, he's currently touring his fourth album, Hurry Up, We're Dreaming, which takes the grandiosity of the Smashing Pumpkins' 1995 album Mellon Collie and the Infinite Sadness as a mere launching point.
So this is the narrative of a man who has fallen in love with a client, but more than this, with the sadness and passion to which he is a mere witness.
Charles Edwards's Aguecheek, arguably the best performance of the evening, is no mere ninny but an aristocratic manic depressive who lends a rueful sadness to the haunting line, "I was adored once too".
In the final scene, the prince's sadness at the loss of Cinderella makes him seem like more than a mere cad.
It is the sadness of a betrayed vocation, since the novelist is someone for whom experience is always mere potential, a way, as Roth puts it in "The Facts," of "springing into fiction".
