I am very surprised that nobody noticed here the free tool named DB2Mon (by Dmitry Liakh)
==> It uses Admin API to get all info on your DB2 instance and db.

I have been using it for years now (currently on a 800GB db with 22M customer and 1000 simultaneous users), it allows a very fine monitoring of your database.
You can easily detect which bufferpool, tablespace or table is too much accessed, or look at the Dynamic SQL tab where you will find those few SQL that issued millions of reads/writes/sorts and requires a serious QueryPlan enhancement.