I also own F5, The Tornado: Nature's Ultimate Windstorm and What Stands in a Storm (my copy of the latter was even autographed by both author Kim Cross and James Spann!), and I also have a couple other books to recommend:
Storm Warning: The Story of a Killer Tornado by Nancy Mathis (about the May 3, 1999, Oklahoma tornado outbreak, with particular emphasis on the Bridge Creek-Moore F5 tornado).
The Mercy of the Sky: The Story of a Tornado by Holly Bailey (about the May 20, 2014 Moore, Oklahoma, EF5 tornado).
And while not entirely focused on tornadoes (it does cover several tornado incidents, but also several other weather disasters), I recommend Mike Smith's books Warnings (about the development of the modern weather warning process) and When the Sirens Were Silent (about how failures in the warning system contributed to the high death toll from the May 22, 2011, Joplin, Missouri, tornado).