There has been issues with SOME aftermarket oil filters causing serious engine damage.
The easiest way to be sure that you don't fall fowl of this, is to buy only genuine GM (Vauxhall) filters.
You might pay a little more for them, but you have to decide if it is worth the risk.
Again, you can get the oil from the dealership whilst you are buying the filter. (This will be the correct specification for your engine)
I use semi synthetic 10w 40, (but you can use 5w40 if the engine does not use oil.) and change both oil and filter at about half the recommended interval - your engine will thank you for it!!
Had the same problem when I first changed mine on my 1.2 2003 corsa,and found it was the smaller of the two choices.It's an easy thing to check when the engine is cold to get a spanner on the filter cap,lift it and check the size,then screw the cap back.The oil that I and most use is a good grade of 10/40 semi synthetic.