This app was mentioned in 2 comments, with an average of 1.50 upvotes
I recommend Andoku Sudoku 2. https://play.google.com/store/apps/details?id=com.andoku.two.full&hl=en
Full version is not free but it's worth it.
No achievements, but lots of variety https://play.google.com/store/apps/details?id=com.andoku.two.full