Don't lock yourself into a length but into the function. I'm new to sailing too and happened to buy the perfect boat for us . . . by accident. Things to look for.
1) Displacement - Can you tow it? (Add the weight of the trailer)
2) Draft - Can YOU launch it? Or do you need a marina and $500.
3) Keel/board type - Can you beach it or do you have to stay in 6' of water?
4) Will you be cruising with it? How many berths? (for how many births)
5) What type of head do you require? Is a porta-pottie in the middle of the cabin OK?
I suggest picking up a copy of "The Complete Trailer Sailor" by Brian Gilbert (or something similar.) Even if you won't be trailering he has reviews, specs, comparisons and sketches (or photos) of about 50 sailboats, 16' to 28', all trailerable. It will help you with selecting the function and the look. For instance, Seward 26 (or 32) is the perfect functional boat, but I just don't care for the look of it. My dream boat (don't laugh) is a 1986 Catalina 27. Except, she isn't trailerable.
Anyway, good luck on you search and have fun.