I’ve used this for years. It works well.
I use the PowerA one.
Get a pro GameCube controller
If you want to use a gamecube controller I'm not sure if ZR will be a button of use this time around, but I'd recommend grabbing this https://www.amazon.com/PowerA-Wireless-Controller-Nintendo-Switch-GameCube/dp/B07GXLBCC3
There's only two Gamecube controllers I'd consider
The PowerA Gamecube wireless controller is basically a GC wireless controller. It connects via Bluetooth and detects as a Pro Controller so it can be used in any game that supports a Pro Controller, though you may want to remap buttons to your liking.
The one downside is that it is powered by replaceable batteries rather than by a rechargable lithium ion battery.
The other is the controller Nintendo releases for Smash. This is just basically a new pressing of the Gamecube controller. Has the GC plug, and you need a GC adapter to get it working on your Switch. In supported Switch titles, it'll detect as a Gamecube controller and it works pretty well in Smash, Cart, Animal Crossing...I'm sure it works in others too. And you can use it on your GC/Wii/Wii U (with adapter) as well.
There are a variety of licensed (from Hori or PowerA) and knockoff controllers online meant to imitate the GC style, but these are cheap imitations and IMO not worth considering.