Automatic Failover without data replication
Judging by your comment, it sounds like you are looking to make the move to AlwaysOn Availability Groups.  The way that availability groups work is that you choose which databases are added to the availability group and are therefore part of the high availability implementation.

So in other words, if you want Database1 and Database2 to be highly available with automatic failover, then you configure a partner to have synchronous commit and be an auto failover partner, and when you create your availability group you add those two databases to the availability group.  But if you don't want Database3 to be part of that topology, then you simply don't do anything with that database regarding the availability group.