Esslingen doesn't have a large body of English-language literature dedicated to it, but several books illuminate the region and the city's Swabian context well.
Hermann Hesse, Beneath the Wheel (1906) — Hesse grew up in nearby Calw and his novels are saturated in the landscape and small-town Protestant culture of Württemberg. Beneath the Wheel captures the repressive atmosphere of Swabian provincial life that Esslingen would have shared. Not a cheerful read, but essential for understanding the region's character.
Henry James, The American and Travel Writings — James wrote admiringly of southern Germany in his travel essays, though he rarely lingered in smaller towns. His broader observations about German provincial life in the 1870s apply well to Esslingen's world.
Rick Steves, Germany — the practical guidebook standard for the region, with good context on Baden-Württemberg, Stuttgart, and the small towns of the Neckar valley. Not literature, but useful for logistics and cultural orientation.