I'm having issues with my flash photography where subjects' faces look too bright and harsh in indoor settings. How can I adjust my camera and lighting setup to achieve softer, more natural light?

I'm using a Nikon DSLR with an external speedlite flash for portrait photography in rooms with mixed lighting. I've tried bouncing the flash off the ceiling, but it often creates uneven shadows or doesn't reduce the harshness enough. My typical settings are aperture f/4, ISO 400, and shutter speed 1/60, with the flash in TTL mode.