When you say your levels of discipline what do you mean? Are you procrastinating? Poor quality of work?
The ‘Selling by the Numbers’ training should help make daily targets that you set feel more manageable if that’s the case, and help shift your mindset.
Books I like around mindset:
-Mindset by Carol Dweck.
-Currently reading High Performance by Damian Hughes and Jake Humphrey
-The Chimp Paradox by Steve Peters
If it’s more around procrastination I can recommend:
-Indistractable by Nir Eyal
-Deep Work and Digital Minimalism by Cal Newport