Currently there are 17 native Standard Prime lenses for Sony A6400 and 12 of these lenses are autofocus (AF) type.
Sony A6400 doesn't have a sensor based image stabilization system but 1 of these Standard Prime lenses features optical image stabilization.
Since Sony A6400 has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 5 Standard Prime lenses with Weather Sealings.