There are a lot of great free mental health resources available online, including worksheets and workbooks that incorporate concepts from evidence-based therapies like cognitive behavioural therapy (CBT), acceptance and commitment therapy (ACT), and dialectical behaviour therapy (DBT).

These sites have large collections of worksheets:

These sites also have several great workbooks:

There are links to loads more resources in this post on Mental Health @ Home: https://mentalhealthathome.org/2018/06/14/mental-health-workbooks/