It might be worth looking at the toilets that have a basin above them, if you keep a toilet separate. The basin is built into the top of the cistern, so the 'flush' button makes the toilet flush (of course) and the refilling of the cistern is done via the spigot where you wash your hands. When the handwashing water goes down the plughole it refills the cistern, if you know what I mean. It's very space-efficient - takes no more room than a normal loo, and it means that not only do people not have to search for a basin, but the handwashing water gets reused (very green) and the fact that flushing gives you washing water encourages those who might otherwise not bother to wash their hands.