To have a fixed setup of workspaces in Ubuntu unity, install the compiz config settings manager and start it:
$ sudo apt-get install compizconfig-settings-manager
$ ccsm &In the
General Options there is a tab Desktop Size that allows to specify the number of horizontal and vertical workspaces. I usually work with a 3×2 grid.
To quickly navigate between the workspaces, use <alt><ctrl><arrow keys>.