Ability to restrict access to particular contacts or deals

We allow all users to view all contacts and deals.  However, there are some large customers with whom we have signed confidentiality agreements that should not be accessible to all users.  At this time, we are not tracking communications or deals for these customers in Sell. 

We would like a way to flag these specific customers in Sell as "Confidential" then define which specific users should be allowed to view and edit the related contacts and deals.  This would enable us to use Sell for these highly important and critical customers.