Confession here: I have literally never drawn Felix in my life. I had to do a ton of visual research to get these characters right, not to mention the style.
And there are SO MANY VARIATIONS! I ended up going with the classic 60's look for Felix and the Professor, a mix of the early original animated and later comic-book versions of Kitty, and for the backgrounds, I took inspiration from the 80's Felix the Cat video game.
Because seriously trying to find detailed backgrounds in the Felix universe is like trying to find a life supporting planet outside of Earth.