I'm not sure what you're looking for (maybe I mis-read your requirements above), but for the step from "I understand the idea of simple boolean logic" to "I understand (quite concretely) how a Z80 (or 6502 or similar) CPU works", I'd recommend the book "The Elements of Computing Systems" from the Nand2Tetris site: https://www.nand2tetris.org/book

It's what made things click for me.

[EDIT: I also second Klelatti's suggestion... Ben Eater's youtube channel is ALL gold. He's an amazing teacher. I also purchased his clock module, and the 6502 kit - they are awesome!]