I think you're right to be cautious of diesels, but they might still be a good choice for an 80-mile motorway commute. It depends how regularly you drive for a prolonged period (more than 30 minutes) at speeds of more than 40mph. If you do this on your commute, a car's diesel particulate filter (DPF) should successfully be able to burn soot off the filter. I'd avoid an early BMW 1 Series, though - they don't ride particularly well and timing chain failures are common. A Skoda Superb would be a good, comfortable choice and there's a wide range of petrol and diesel engines available.