I haven't used Ubuntu for over a year, so I don't remember the details. But you can definitely assign a keyboard shortcut for switching between maps (I used Ctr-Shift). Check your system settings, either in the international keyboard mapping section, or where you can set keyboard shortcuts. Or failing that, ask your question on the Ubuntu support forums - you'll surely get an answer there.

Yes, I can type the characters anyway (see above), but with a special layout for Esperanto (that doesn't produce > when I want to type :, and things like that) it'd be much more comfortable.

I've now asked at the Ubuntu Forums: http://ubuntuforums.org/showthread.php?p=6817944...