>> do I need to trademark my domain name even if there is no current business out there using the same name.
You should first understand that you technically can't trademark a domain name. A trademark can protect your business name, or the names used to identify your products or services. So you'd register your business name as a trademark, not your domain name. By extension, then, your domain name is protected because it contains your business name.
For example, if your business is Widgets World, and that's how you identify yourself in conducting business through your website at widgetsworld.com, you'd register the name "Widgets World." If someone else came along and registered widgetsworld.net, they might still be found to be infringing on your mark in a domain name dispute.
You'd only be able to register "widgetsworld.com" as a trademark if that's the name under which you conduct business. If your invoices and letterhead use "Widgetsworld.com" as your business name, it's a trademark. But it's not if it's just your Internet address but you identify yourself as "Widgets World, Inc."
It's a subtle difference, admittedly, but one that should be understood before you start spending money to pursue registration.