Spreading Load on SQL Server database

Spreading Load on SQL Server database

We have an enterprise application that uses Microsoft SQL Server as the
database backend. We have been coming across a fair few instances where
the customer has grown the application into a huge db and some of the
queries being run are causing locks and performance issues for themselves
and the other users.
We have tried to apply as many indexes as possible and perf tuned all
queries too the limit but we have one application that must suit a lot of
different customer types so its hard to create one solution that fits
all.We dont have the resources to apply customer specific
indexing/performance for every customer.
We know the main queries that are causing issues are the ones that are
generated to drive reports and kpi's.
My question is, is there a way that we can spread the load of the
application so the day to day use isn't hampered by the report/kpi
generation. i.e. Could we someway mirror/duplicate the db so that day to
day actions are sent to SQL Entity A and the data intense queries and sent
to SQL Entity B? Therefore the data intense queries have no effect on the
day to day side of things and we could queue the queries going to SQL
Entity B.
In this scenario SQL Entity A and B will need to be kept in alignment at
all times, but SQL Entity B will always be read only.
Can anyone suggest any paths we could try to accomplish this? Or is there
another method I should be looking at to get us performance wins.
Thanks