All uses of juju.Conn other than Bootstrap and Destroy require a state connection, so make State an exported field of Conn and connect to it when creating the Conn.
The few places that call Bootstrap can easily call Environ.Bootstrap instead.
Also add environs.NewFromName to make it easier to open an environment, rename juju.NewConn to juju.NewConnFromName, and add juju.NewConnFromEnviron to join the dots.