Alpha Omega, A Beka, BJU, ACE, Basic Christian Education, and Landmark Freedom Baptist all sell workbooks for high school. All of those are Christian companies. I can’t think of any secular workbook publishers off the top of my head, though I’d guess there probably are one or two. Hope that helps.

We did SOS for my oldest. For my kids, I’ve found that it’s best if I can keep as much of their school day off the computer as possible. There are too many distractions when their laptops get turned on.