Castrol makes the oil for BMW motors nowadays. It's maybe even cheaper than amsoil and covers all relevant standards such as LL01. Unless you have shares in amsol or something I would just buy Castrol.
https://www.castrol.com/en_gb/united...duct-page.html
But if you're going by frequent change intervals and use OEM filters, I wouldn't sweat what oil to use as long as it's fully synthetic.