I've been washing my hair with just water, and it works better than I expected. In the past, if I didn't wash my scalp before bed I'd feel itchy and sleep badly, but water seems to do a sufficient job of convincing my brain that I'm clean. When I feel sufficiently gross I use shampoo anyway. Conditioner is required to get a brush through it; my hair is very curly and will form knots if not brushed.
I am not planning on ceasing to use body soap.