Thanks for your interest in developing gaze interaction applications! Indeed, from your description it sounds perfectly suited for the Core SDK Interaction API, so you should not need to upgrade to the Pro SDK.
There are many sample applications bundled with the Core SDK which you can download @ https://github.com/Tobii/CoreSDK
And an extensive tutorial and user guide to follow online as well @ https://tobii.github.io/CoreSDK/
Good luck and please consider publishing on the forum your software!