I can't see the glow plugs being the problem - I suppose slow starting might mean a little more soot going down the exhaust, but not enough to explain dpf problems.
Mine alarms/warning light about every 3 months as I only use the car for a short commute. Occasionally it tries to do a regen if I go further afield. A cruise along the M4 to London works nicely (it usually goes into regen around Reading), but sometimes it decides to try one when I'm only gone a few miles up the M5. I can hear it trying to regen in queues. Fuel consumption shoots up, and engine sounds really rough. You can tell it is doing it if you put the data on "Range" as it tracks mpg every few seconds.
I 'fixed' the problem by buying AlfaOBD and installing it on a 7" tablet I use for work. Software cost about £35 - I imagine one trip to the garage would cover that? When the engine light comes on, I run a forced regen myself usually somewhere remote as it is a noisy process.
I have monitored the process (using the AlfaOBD) and the forced regen definitely works best if the engine has barely warmed up. It will get the dpf to 700 Celcius, and the pressure reading drops back to 5mbar (i.e. the filter is clear). Once the cycle is over, I drive home in 2nd gear at about 3600 rpm as the dpf is still hot enough to burn off the soot.
Running a regen when the engine is hot, I find I usually have to do it twice. No idea why, but the temperature only gets up to 400 Celcius.
One last thing - the condition of the oil is part of the computer's decision making process as a regen messes up the oil (I think it dumps raw diesel into the cylinders at the wrong time so that unburnt fuel gets down to the filter). If you do an oil change, you'll need software and an OBD link to tell the control system you have done it.
When I got the car from my brother in law, it was on 100K, and the oil change procedure had not been run since 26K, despite him using 'proper' garages. This causes the oil light to flash for about 30 seconds after start up (presumably to tell you that as you haven't changed the oil for ages, it won't be doing a regen any time soon). Seeing the oil light flashing, he took it in. The mechanic charged him cash (basically to check the oil level and look for leaks), and never thought of Googling "flashing oil light multipla".
Anyway, to sum up...buy AlfaOBD plus OBD link (or similar). Take car for short drive. Read codes (I think 1206 is the one you are looking for). Clear codes. Run "regeneration". Change oil. Run "oil change" procedure. Always take device plus link if going away for a few days.