I feel no such vibrations. Almost sounds as if you are getting a miss under load. To get enough motion through the motor mounts, through the body, through the seat to your bum would take quite a lot of force. Suggest a dealer visit for sure. My car had logged a miss on two cylinders in the OBD, found it with Carista. That's a good use for an inexpensive scanner... checking for odd things the car may encounter.
But to be sure I better go for another drive! Great excuse.