How do I add a little bit of personality to my SOP without turning it into another "trembling steps" narrative?
I received similar feedback from a professor who doesn’t subscribe to the “trembling steps” narrative, so I felt it was advice worth following. I navigated the problem by adding a “because...” to a few of my sentences. So you could say something like “I did research on X for [number of years] because I feel it is important/worthwhile/interesting etc.” You’ve prepared yourself for grad school and have lots to show for it, so if you start thinking about why you decided to do those things, it’ll make it easier to add a “because” here or there, which should make your statement stronger. 

Think about your field and what you want to contribute to it. Why is your field worth studying? What makes it important? How are your unique attributes going to advance your field?

I would avoid directly saying something about yourself as a person. The wording of the statement should be enough to convey your voice, and your accomplishments discussed in the letter speak enough to your personality and passion. Just like in creative writing, show don’t tell. Ask yourself what you want the readers to know about your personality, and rephrase your existing sentences in order to convey that sentiment if you feel it is lacking.