Conversion Tracking

Does anyone know if there is a universal URL for the final thank you page of the check out process?

the http://checkout.spreadshirt.com can be used in your settings, but every customer recieves a unique URL.
So I´d suggest to not use the term “matches exactly: http://checkout.spreadshirt.com” but to use “contains: http://checkout.spreadshirt.de/

Question: Is there a certain reason why you would like to have a customized tracking funnel?
Usually the default set up of your shop is coming with all relevant data and will forward it to Google Analytics