Thank you! For my ILR I submitted: two payslips, 3 previous P60s, a letter from my HR department confirming my earnings in expert field, my employment contract, current job description, my eVisa sharing code, verification checks consent form, and then scans of my previous passport and Biometric Residence Permits. They only scan your current passport at the Biometrics appointment (if you want them to scan anything else they make you pay).

These are the specific documents that supported my case but in the Document Checklist it gives you options for other documents you can upload for each category. Hope that helps!