I second skoda-parts.com, very good service, good quality parts with credible non-OEM alternatives.
I do use autodoc from time to time, if you know exactly what you want, it is a good source of inexpensive parts and what you order is exactly what you get, at least so far for me. The trouble is you really cannot rely on the list of components produced for each oem part number typed into autodoc search to provide you with exact like for like replacement for the oem part. But if you know exactly what you want (as in from which company, ideally also with manufacturer's number as well as VW/Skoda number), e.g. brake discs can be had much cheaper, and with premium (geomet) coating, there is also much wider selection of e.g. tailgate gas struts and airco components.
Skoda-parts is much more reliable in this respect,e.g they will show you Bosch injectors at a third of the price alongside exactly the same Bosch injectors with VW/Skoda number on them. Plus you can filter parts quite well by the car's VIN number.
Back to the topic of glow plugs, I have been using NGK glow plugs for some 10 years now on 3 Skodas so far, including the vRS, the NGK ones heat up faster, glow hotter, and last at least just as long as OEM Beru ones, plus they take less current, though this was biggest difference on older models, like 2.5TDI V6. For plugs without sensor and the 2.0TDICR as in all Octavia vRS TDI engines, I think latest part number is Y1002AS or 8926, they are widely available, though on my last change I have used older parts Y-609AS 5849 on both the 2.0TDI CUNA and the 1.6TDI CAYC. For the pressure sensor plug, I always get the VW/Skoda part, last 2 from skoda-parts. Note that the single pressure sensor glow plug will be 3x-4x the price of all 3 remaining glow plugs... VW price gouging.
Always replace glow plugs on fully warmed up engine, and do not exceed maximum undoing torque (2-way click torque wrench is helpful), if they don't go out at max torque, put some engine oil around the plug, try a couple of times more then leave it for a week of driving, a few thermal cycles plus the oil will loosen it up. Usually, what snaps the glow plugs is trying to undo them at too high torque on engine that is too cold. More info here