Making it a furry

(i don't draw realistic so if you're talking strictly realism i'm sorry LMAO)

For fluffy necks theyre pretty fun, it helps to sketch the base shape of the actual animal anatomically correct, then to emphasize the fluffiness add multiple layers of fur. Make sure you keep in mind when the fur changes direction! You can use different shapes of tufts to give the illusion of softness or sharpness. Keep in mind where the other muscls like the shoulder and head start and how their movement/pose changes the fur. It REALLY helps to use references Heres an example I just threw together:

For a cat on its back legs, I suggest making the basic structure kind of anthropomorphic. I'm sure you can find some references online, but basically making the back legs thicker might help with what you're looking for, personally I don't drawn anthro tho i've only drawn them once :')

Goodluck! hope this kinda helped a bit :)