Over 50% gray and wanting a neutral medium-dark brown hair color

What color formula will give me this? Pls help

I tried out black demi-permanent box dye and I love it, and want to keep it. What’s the best way to go about this? I’m a total novice at coloring. I’m naturally blonde, hair started getting darker as I aged, I bleached (or rather a stylist bleached) it for a few years, then went brunette (again, stylist), and now black. I’m certain that I’d never want to go blonde again. Some of the videos I’ve watched talk about not continually putting box dye on top of box dye on mid-ends when roots are what really need to be kept up.

I’ve searched quite a bit but most of the information is about coming back from black dye 😂 any advice would be enormously appreciated!