Not to rain on anybodies parade here; a First Class Medical determines that you are medically fit to fly and airplane, not that you can reach all controls.
XL has similar problems to S. Airplanes and especially training airplane are built to standard sizes. A C172 with a cushion can be pretty uncomfortable.
A C172 is more suited if you are too tall then on the shorter side.
You may need to shop around a little more for suitable airplane types.