Alas, Sixth Grade Math With Confidence is the last level of the series. Fortunately, Kate Snow, the author of Math With Confidence, has given a very thoughtful and thorough answer to this question on her website. Please click here for her recommendations.
https://kateshomeschoolmath.com/what-to-use-after-sixth-grade-math-with-confidence/
The Well-Trained Mind Press, publisher of the Math With Confidence series and owned by Dr. Susan Wise Bauer, also highly recommends the online courses at The Well-Trained Mind Academy. Dr. Bauer is passionate about providing high-quality instruction from great teachers. Check out the textbooks chosen as the spines for their courses.
For post-elementary, pre-Algebra math, some of Dr. Susan Wise Bauer's recommendations include Math Mammoth, Math-U-See, Right Start Mathematics, Saxon Math, and Singapore Math. The one that is best suited for you depends on your student's learning style, strengths, and weaknesses.
If you're looking for more recommendations, check out our Curriculum Recommendations Portal, where we have curated lists of thousands of high-quality curricula and supplements.