I've followed the directions here to disable the magento system cache, but am still forced to manually clear caches each time I change something in CSS. Slowing things down quite a bit!
Note: two of the cache types mentioned in the post do not appear on my admin cache management page: View files fallback and View files pre-processing do not show up.
Did you try to put in "Stores/Configuration/Advanced/Developer" at "Frontend development workflow" the value to "Client side less compilation"? Also in this mode you are forced to manually clear cache?
I would suggest to use grunt watch together with LiveReload to automatically track for changes and recompile LESS files. It will also generate sourcemaps.
Check out the documentation at http://devdocs.magento.com/guides/v2.0/frontend-dev-guide/css-topics/css_debug.html