Just for the info, you might consider downloading the sample of middle school astronomy from Real Science 4 Kids. It might work. You could bump it up to high school level with a research paper or two. Upside is you'd have labs and a teacher's edition. Downside would be cost and I doubt you'll find it used because it's only been out a few years.
It's toward the bottom of this page. Focus on Middle School sample chapters.
https://gravitaspublications.com/get...arted/samples/