I recently subscribed to Prologue, so I can read the entire magazine (as only certain articles are available online). One of the small features in the Spring 2009 edition was called "Bess Truman's Hat." The Truman Library has 55 of Bess' hats as part of the collection and one was featured in this edition. Rather than that artifact (which I couldn't find an online picture of), I found this photograph from the Truman Library of of Bess Wallace in 1911.
The small article in Prologue asserted that Bess loved hats. They quote a friend of hers as saying that Bess, "had more stylish hats than the rest of us did, or she wore them with more style." In addition, they quote Bess (who definitely did not enjoy being First Lady) as saying that a woman's public role was, "to sit beside her husband, be silent, and be sure her hat is on straight."