Oday 23, 25, Catalina 25
I don't know what your budget is, but my personal favorites that meet your criteria are the Oday 23 and 25, and the Catalina 25 (pop-top model). The Oday 23 is the only boat I found less than 25 feet long that has a "separate" head. All of the other models I saw had a curtain at best for privacy. 5'6" headroom on a boat that small is asking for a lot, especially if you want the boat to be trailerable. Remember, headroom on a boat that small usually means a deeper draft and/or higher freeboard, both of which work against your other goals of trailerable and easy to swim off of. The Catalinas have a great pop-top design, better than the Odays IMHO, and pop tops are a really neat way to get full standing headroom on boats that otherwise would accomodate it. I bought the 23 for a few reasons: keel/centerboard (ballast in permanently attached shoal keel), as opposed to swing keel (ballast in movable centerboard); big cockpit; good quality construction. I don't trailer my boat, so weight wasn't an issue, but I have been told that they are a bear to tow. You can't use the family car, you need a real truck with a towing package. This will be true for any "trailerable" boat over 20 feet that does not use water ballast. Its not that difficult to swim off of the 23, you just need to buy a $40 swim ladder and take down the lifelines. There are a lot of great boats that meet your needs, good luck and have fun.