Yes. You can use multiple QuickBooks account, Armour8192.
Just a heads up, the system allows you to add one company per subscription. That being said, you'll have to purchase a different QuickBooks account for your CIS self-employed business.
However, we can use the same User ID and Password. This way, it would be easier for you to switch between accounts.
I've added this reference on how you can switch accounts: How to switch between companies?
I'll be around if ever you have other concerns. Have a good one!