How to document continuous usability testing for monitoring over time?
Current situation
Our product is almost being released to the first group of customers after a successful pilot phase. We are regularly performing usability tests. The results are a snapshot in time of the current user experience and function as a basis for further development. I create an individual report with user feedback and related improvements and their priorities. After my team has seen the report and we defined related activities and user stories the report has no value anymore and can be disregarded. This works well for now.
Future need
However, I would also like to track the high level overall quality and user experience as a basis for strategic more high level decisions and to monitor performance over time. I couldn't find any examples let alone best practices of how to document this. I'm looking for a solution that is easy to access, update and analyse as well as being lightweight.
Can anyone point me in some direction?