Hi Nick
I would be tempted to agree with the suggestion of a larger tyre profile as it is the first point of shock absorbance and the higher the profile the smoother the ride.
Maybe best to keep the 19" rims, fit spacers and go higher profile (e.g. 45 or 50 profile) and not bother with runflat feature.
Let us know how you get on with it all
Cheers, Trevor