Jay Babina's Outer Island is another good candidate. It's a Greenland style boat with plenty of room for your feet. It's a stronger tracking boat than the Night Heron, which is very maneuverable for an 18' boat. Either one should do the job.

To elaborate on Shawn's point about foot braces:

I initially had foot room problems in a lot of boats, as I tried to set my foot braces so that the soles of my feet were perpendicular to my shinbone. This position requires a lot of foot room and also creates constant pressure on your feet. The result was cramped quarters (even with my feet splayed) and sore dogs by the end of a trip. On a whim, I cut some 15 degree wedges out of 2x3 stock and screwed them to the pegs, then set them forward one extra notch. What a difference! They provided more support, more room and far less foot fatigue. I now set the foot rests in all my boats such that I have to angle my feet forward substantially in order to contact them with the balls of my feet. That way, I have all the room I could ask for, no pressure on my feet while cruising and can push on the foot rest quickly when necessary. It's really made paddling much more comfortable. An added bonus is that you also have less pressure on your back when your feet aren't hard against the pegs, so back comfort is increase, too.