how to save state as new workspace

I recently had one of my most complex and important workspaces open, 
then closed the windows, and got searching for something else, which 
led to several new windows each with  a bunch tabs. Now, I would like 
to save as a new workspace for the new project.

You would think there would be an obvious way to save such a state as 
a new workspace, without altering the previous workspace (which is 
still active). But, when I have tried this in the past, the result 
has always been frustrating. I either end up losing my new work, or 
overwriting my old workspace.

Can someone explain exactly how to go about this.