You might check out Tom Yost's site - He has offsets for most every kayak he has designed there, and all of those will tell you the respective deck heights, for each design, anywhere along the boat. Check out pics of the various designs in use, and pick one that looks about what you feel comfortable with (i.e. - do you need lots of foot or leg room, or not?).

You might sit on the floor, rather than a chair, and see what a comfy knee bend angle is - and how high that is, too.

My boats aren't close at hand, or I'd just give you the measurements directly.