[ssivark]

There's also the Tufte style layout, latex template here: https://www.latextemplates.com/template/tufte-style-book

I think works really well for textbooks, with well-placed footnotes, sufficient margin space to make notes, etc.

There are, of course, many other styles, if you do not wish to utilize page area more efficiently.

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If you need nice equations (or even just Greek alphabet), and a no-hassle reference linking system, I can't think of anything other than TeX derivatives that will do a good job.

PS: If OP wants more useful suggestions, we need to know the topic and/or what kind of content the book will contain -- text, equations, floats/figures, photographs, etc.