Morning James
Welcome to the Forum
The only Daft Question is the one you wished you'd asked
BMW specify a range of oils for use in different climates check the hand book. 5-30 fully synthetic is normal in the UK and Europe, 5-40 fully synthetic in extreme conditions (Heat) or in a very high mileage engine
I use Castrol Magnatec so does my Brother Inlaw in his diesel
Hope this helps
Dave