Welcome to Sailnet!
That's a tall order -- trailerable, head, cooking and sleeping accommodations, diesel engine inbord, 17-22 feet.
Over here in the States, we have a couple of boats that the trailer-sailor cruising crowd always seem to speak highly of: Montgomerys
, and West Wight Potters
. But unfortunately they do not run an inboard diesel -- just outboards.
I'm not at all familiar with your waters. So I'll just mention that the Montys and WWPs are very much on the lighter end of the spectrum -- good for trailering/launching but maybe not so great for any real serious ocean work in rough conditions.
On the other end of the spectrum would be something like the Flicka 20, built by Pacific Seacraft. But these are built heavy enough to cross oceans, so might be too much boat for your purposes. However, there are plenty of folks (likely the majority of owners) who use them simply for coastal sailing. Here's an example:
Flicka 20 by PSC
Good luck with your search. I'm sure you'll get plenty of suggestions -- everyone seems to have their favorites.