Your question is too general. Tools that you use depend on the problem that you are trying to investigate.
SQL0911N could indicate either deadlocks or lock timeouts. For the former you use the deadlock event monitor, which has very little overhead and is created and enabled by default - all you need to do is to read the files. For lock timeouts there is additional monitoring that was introduced in DB2 9.5 - you can read about it here:
Lock timeout reporting
You should explain to your bosses that there's no such thing as free lunch. If they want to monitor the system all the time, they will pay the price of performance impact all the time.