Oils ain't oils

If you are my vintage you'll remember the ad about car engine oil.
Well since then things have only become more complex and after yesterday update one could only wonder if there is a bit of the old BS thrown in as well to muddy the waters.

I have a 2014 Citroen C3 1.2L Seduction Petrol and I'm about to do an oil change. I went to two of the biggest retailers to get the "good oil". The first guy went to a lot of trouble. Looked up the computer and came up with Penrite 5W40 synthetic.
I then said the car had been serviced by Citroen with their own 5W30 synthetic. He then called Penrite and spoke to a guy who said 0W30. He and I were confused so he looked up another major brand and they said 5W30.
OK so we sought of averaging 5W30 then he added another layer I wasn't ready for - additives.
What does that really matter that much, I said? Yep it does he replied.
In the end I said look maybe I'd just be better to go to Citroen and get their stuff. He agreed maybe it wasn't a bad idea.

I hate to be controlled and I wondered if the additives are really that important so went to another very big retailer. The first guy wasn't too knowledgeable and walked me over to the most expensive 5W30 and said that's the one for you. Wanting more info I asked him about a 5W30 synthetic on special. He replied not the same additives. When I asked about how important it was he then got the another guy who looked like he could be the manager. He looked up the specs said I could use 5W40 synthetic, 5W30 synthetic or mineral.
So mineral is OK now then. In the end I bought an oil filter and no oil.

I live on South Coast NSW and the climate is not extreme.
Since I'm not one to rev head it about, could I use mineral and how about the additive bit?
I'd say the local mechanic would just use 5W30 any brand or additive or am I wrong?

me - I would follow the penrite tech guru's advice.

I have thrown the penrite company a lot of curly questions over the years, and they have replied using "non tech speak" that explained the whys and why nots and being a great help.

Ended up following their advice - saving bucketloads of money, and engines / gearboxes / transfercases /cooling systems and P.T.O's running trouble free.

What grade did Citroen specify?