Once upon a time, I used to feather in the edges manually. Using Photoshop Elements. This is necessary almost without exception with hairy critters whose hair fades to invisibility at the ends. I invented a trick. I make a duplicate image layer, use the "average" effect (turns the cutout uniform) and then the "find border" effect. So I have an outline. I can increase the contrast and blur it (to make it extend further inside the original outline of the cutout) also and then select the blurry outline. Then I apply the selection to the original cutout and run my eraser around the edge at 30-50% and then blur the result of that. (Not to mention that it took me a fair amount of time to discover I could use one layer to select, then apply that selection to another layer.) (I began the project with Sqirlz Morph software.)
I get greater control than with the "feather" tool.