Bridgestone or Dunlop Runflat 3s, which ride as well as standard tyres due to different runflat technology. But you will need to replace the whole set. You can't have one different type of runflat on one end of the car and another on the other. I never ever recommended substituting standard tyres. That's the way to get killed changing a wheel on the hard shoulder (as I very nearly was, once, despite protection from a police car).