Hi there! I’m you. My first computer was a TRS-80 in the early 80s, and my daily driver today is Debian (a flavor of Linux). I’m not an IT person, but I’ve had some skin in the game for a while.
You won’t need to purchase a thing unless you have some weird/old hardware where drivers will be a challenge.
There are a million flavors (“distros”) of Linux. The most straightforward ones to start with are probably Ubuntu and Mint.
Most Linux distros have a “live CD” version that you can “install” on a thumb drive. That allows you to take the entire OS for a test spin without changing anything on your “main” computer.
+Roquefort gang.