Migrating DB, SSIS packages, SSRS Reports from 2008 R2 to 2012
You have a lot of reading and testing to do.  There isn't a magic bullet per say but lots of ways of hitting this issue.  Firstly setup the 2nd environment as if it were prod, but restore the databases in a test environment and restore the SSIS packages.  If reporting services are not dependent on this then focus on this part first.  Give your SSIS package test data to feed and test the validity of the data.  You can even have it write to a test table using your business logic, and have the real process do the same thing so you can ensure you get accurate numbers and figures.  

Mirroring is a fine solution assuming you're fully up to date, but there's 2 modes to mirroring and high performance is only available in Enterprise.  Thus your network has to be fast when you setup mirroring since all transactions must commit on the mirrored side first.  

Are you following all the 2012 upgrade best practices, best practices analyzer, upgrade wizard for code issues, researched potential codes, have a well written test plan, and acceptance tests?  

User Kin answered a very similar question, so please do research this site for info or duplicate questions, you'll often find a lot:

For SSRS depending on the complexity, you might want to just rebuild it.  If you wish to migrate, the SSRS Scripter is a great resource. Kevin Klines "how to" and "how to migrate reports" are also included in the link.