Hello Wesley,
You are correct. If you only need the R2 button to perform Rapid Fire then your choice would be PS5 Controller plus Rapid Fire added.
Here is the link below to purchase your controller.
https://megamodz.com/PS5-Custom-Controller
Quick Visual Instructions:
If you also want to be able to set up Rapid Fire on R1 button, then additionally you'll need to purchase the Layouts feature.
We also offer Advanced Back buttons, that allows the user to first pair any controller stock buttons to one of the paddles on the back and than make those assigned buttons to act as Turbo Buttons. You're just holding a paddle and modchip repeatably presses an assigned button as long as you're holding it down.
More information can be found by link below.
https://megamodz.com/PS5-Controller-Paddles