If you are a sole proprietor, then from a legal point of view it does not matter if you mix personal and business in one bank account, as the legal ownership is the same. It also does not matter from a tax point of view, as there is no reporting of assets (bank account is an asset) in the tax return - just schedule C, which is the P&L.  From a personal tracking point of view it's a good idea to reconcile the bank accounts, so you should not exclude transactions, as if you do, you can't reconcile.  You can even categorize personal expenses, under "Other Expense" type accounts, and post business expenses as regular "Expense" type accounts, and then the Operating Income in the P&L (which does not include "Other Expense" accounts) is the taxable income, before adjustments, like mileage.

If this is a corporation then, you should not mix personal and business in one bank account, mainly because you may lose the personal liability protection that you get with a corporation.