You'd think the main stealers would know what they're at. I can read the soot levels in my motor with my €30 (VAG specific) OBD Eleven device. AFAIK, if it doesn't regenerate at 24g and return to <=6g after regeneration the filter is fucked and needs to be replaced, althogh there are specialists who advertise reconditioning. Anyway, I haven't had an issue with mine yet. Hopefully, the bit of motorway driving I subject the motor to will keep it that way.
Are you using the correct grade of engine oil and changing it in accordance with manufacturer recommendations? Our bog standard EN590 diesel is as low sulpher as can be got so I don't see any point in paying more for something that's no better. In fact I bet the "better" stuff is EN590 as well! However, oil quality is apparently relevant to DPF soot levels.