As far as comfort goes, have you looked in to a recumbent design? I run a "recumbent" and it is nice for cruising, it would be easy to to do to any 26" bike, You just have to modify the front fork and put a 20" wheel on it. But a nice comfy seat on it and away you go, if you ever get tired of it, swap your forks out, put your cranks back in and change your seat.