On your original installation, you can open a terminal and run:
sudo apt-get install xfce4 xfce4-goodies
That will give you the equivalent of a fast-running Xubuntu desktop with all its configuration options, plus all the software of Ubuntu. That includes LibreOffice, which is superior to the Abiword/Gnumeric office suite of Xubuntu.
FWIW, that setup has been my preferred arrangement for some years.
Edited: I should add, when you do install that, the login screen will show, above the password box, an Ubuntu logo. Click on that, and you will see you have the option of using either the Unity or the Xfce desktop.