Take my hand, I am only 19!
https://i.imgur.com/6PCX4Ti.png

I used this (it had plenty of trim included to cover a not perfect cut. My obese cat manages to get through even though it was to just let the thin one through). https://www.amazon.com/gp/product/B079QPL57P/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1