Thumb Grip Caps for Switch 2, 8 Pack Silicone Joystick Covers, Soft Touch Analog Stick Caps with Raised Dots, Protective Thumb Grips for Better Comfort and Control

Personally I love these ones from PlayVital - if you think you just want a flat cap then I'd recommend you just get these: https://www.amazon.com/dp/B0F7RHSJ3Z I did find a pretty cheap brand if you want to save some money instead, but I was too scared of the lack of reviews to try them myself. I doubt there's a cheaper option than these on Amazon, though: https://www.amazon.com/dp/B0GRFWNHPG