There are lots of good textbooks. I will list some, free or otherwise.
Online textbooks
Paid online textbooks
- TextFugu by Tofugu!
- 80/20Japanese available in physical, audio and online form.
- Mondly is not technically a textbook. It’s similar to DuoLingo or Rosetta Stone Japanese.
Physical textbooks
These are available from Amazon for cheaper, the links are to the official sites.
Kids books and native support