Automated report to know who has been added / removed from site and org admin without having to enabler loggers which can fill up logs quickly

Need a way to either schedule the report to get who added / removed users from site admin and org admin groups. Or this should print the details in logs without having to enabler lot of loggers which can potentially fill up space pretty quickly. This is extremely important because, we have a process which is driven by security to get the access , but without approvals if we see someone getting added even if its intermittent, we want to know who is performing such actions as its breaching the policy