The best template for self-appraisal is to instruct junior employees to demonstrate their performance. At the time of the Performance Appraisal (PA) meeting, they should provide adequate evidence of their performance. The manager should only validate the evidence.
However, this is much easier said than done. For this, you need to design proper KRAs and hand them over well in advance. To help employees understand what KRAs are, you need to create a sound policy on the Performance Management System (PMS) and train your employees on it.
You have written that "My company has little trust in performance appraisal." Who does not believe in PA and why? Isn't people's performance a route to measure the organization's performance? How will your management be able to elevate organizational performance without improving people's performance?
I have been writing on PMS or KPIs and KRAs through several threads. You may check the following link to clarify the concept:
https://www.citehr.com/526357-kpi-kra.html
For further queries, if any, you may call me on my mobile.
Thanks,
Dinesh Divekar