I recommend having a look at the books by
下村昇
There are inexpensive kanji references and workbooks for each of the 6 grades.
He has an interesting system for remembering a character based on its graphical etymology and breaking down the kanji into smaller elements to make a sort of spelling rhyme.
He also authored the doreamon 1006 kanji book, which is convenient as it's a single book but the detail of his other books is better.
The kanken step books are also worth looking at. They're Yellow and Blue but I think you'll find them in the adult section rather than the schoolbooks despite the majority being for school level kanji. 10, 9, 8 級 coressspond to Grades 1, 2, 3. The kanken tests could provide you with a target for kanji study too. Since you (untmdsprt) work at a school you could probably sit it there ask the 国語 teacher.
What I have found about schoolbooks is the vocabulary tends to be at a higher level than a second language learner might have. Maybe it raises your game but it's something to be aware of.