Good call from Rhys. S2 makes a number of boats -- tho their numbering system prevents me from recalling which ones -- with something like a real enclosed head. A couple of their lifting keel models use the keel box as one wall of the head compartment. As a bonus, S2s tend to sail pretty well.
And of course, the Mac26 powersailors have a private head space. Set up for a portapot, but you might fit an electric or manual head in there. Remember, tho, that a head needs a holding tank, which is bulky and difficult to site on a small boat. Many higher-end portapotties have fittings to plumb them for venting and pumpout. That, IMO, is where you ought to be looking.
Dedicated heads take up more space than than trailersailers offer. Hell, I'm having fits trying to physically fit a head on a 30'er, and whatever we come up with, it will be semi-alfresco. There is no expectation of privacy on a small boat. Shy bladders need not apply.