For sole proprietors there isn't a legal requirement stating that you have to have a separate business bank account, although it is recommended to keep personal expenses separate from business.
It might feel like more work to open up a business bank account but in the long run it will save you alot of time and time is money!! Using a personal bank account means you will have to separate out personal and business expenses and keep track of what is persona and what is a business expense which can also cause headaches at tax time and who wants a headache right?
If you separate your personal and business bank accounts you will have a much cleaner more organised income and expense tracking system. You will also have a clear snapshot of your business expenses and finances. This will also help when dealing with your accountant as you will have a separate account for personals and business and you will also have clear reporting for each.
Having a business bank account will help your business to appear more professional to clients, businesses and the tax office when you need to lodge those tax payments!! Lets face it if you want to take your business seriously then treating it like a serious business is an important step in the right direction!!