Change credit card on icloud storage

HOW DO I CHANGE THE CREDIT CARD MY ICLOUD STORAGE IS BEING CHARGED TO?

This is about using a business cc for business purposes and a personal cc for personal purchases.

The recommended doc 'Change, add, or remove Apple ID payment methods - Apple Support'

does not seem to explain how to change the card being charged just for iCloud storage. But it allows a change only for all purchases.

For example, I use iCloud storage for business and Music for personal use. I can see how to change the priority order. Do I have to check and change the priority order each time I make a purchase, or can I set my business card as the default credit card for icloud storage and my personal credit card as the default for all Music purchases?

I have tried on both iOS and Mac OS but cannot see how to do this.

Do I have to create two Apple accounts - one for business and one personal?

If so, can both accounts access common areas - such as contacts? Or do I need to split my contacts into two - business and personal?