I have a 3series Saloon M Sport with 18’s.
I switched from a full set of run flats to a full set of non run flat michelin pilot sport 3’s approx 2 years ago.
A Full set of run flats where costing approx £1000, non run flats £700, but i got a set from costco for £560 (20% off offer)
Conpressor & Foam combo in the boot should I have any problems.
I would say the improvement in ride quality is marginal, not a big as people make out. Also looking on the net the recommended pressures to run non run flats seem to varies greatly!
I would personally recommend the switch to non run flats but remember to get tyres which are XL rated sidewalls.
Edit: I just improved my AA cover for worst case scenario of a blow out.