While not wanting to sound un-empathetic, I would like to draw your attention to the fact that most GA type aircraft are structurally designed to accommodate a person if 170 pounds. The aircraft is carefully designed to protect it's occupants in a crash. It will restrain and protect in a 170 pound person in a 9G (rather low force) crash. Any amount of body weight above that, and the restraint capability, and capacity to protect you, are reduced by that factor. This is of an added concern, if two large people occupy the aircraft, as some seat belt attach points in the structure are shared between the two front seats.
It interests me that in the loading limitations for an aircraft, their is most often a maximum permissible weight (approved capacity) for anything to be carried, other than a person, and the persons are who we are most trying to keep safe.
Please consider carefully what you are asking the aircraft to do, relative to what it was designed and approved to do. Are you comfortable having much less personal protection than was designed into the aircraft for a person who is described by the standard?
Your ideal training aircraft would be a Cessna L19/O-1 Bird Dog. Though rare, they are out there. They are very roomy in each cockpit, for a light aircraft, and lots of fun to fly too!