THe misunderstood floor sack points out that in order to achieve a realistic behaviour of an animation you have to consider the underlying structure of bones and muscles.
If you go to stretch and squash it really far you can achieve a cartoony overdrawn look.
The floorsack is a practice for shifting masses, rather than for giving something a personality
The basic problem we are facing here is the constructive approach of drawing and observations coming from the anatomical side of art added to simplified models.
This means that the big forms of any character have to be established (or at least considered in a static state) before squash and stretch is added, in order to keep the illusion of space convincing.
If I look over your kitten it seems to be made out of a big conical cylinder.
I did this quick basic drawing of the forms to show you which basic considerations I made.
3 baseframes of the initial sketch constructed on top of your design - pretty jerky
+2 inbetweens - 8 frames now with the loop - so we already got a good fluid animation on 2's
adding the up& down movement to the steps and here is start to add weight.
As you can see every step is now reduced to 4 frames (there are 2 dons and 2 ups in the animation)
now the limbs can be animated (or you could decide on adding more frames before this, if you have to add them afterwards you might have to redo some animated parts)
removed help lines for a better view (otherwise the same as the image before)
as you see this rough animation has so far no squashing and stretching applied, the construction lines are still and the whole body lacks movement.
Although it's of utmost importance to reach this step with solid forms (or at least consider it in your mind) before you add any stretching or squashing.
If you add it, without considering the main forms it looks like your sack (there is no underlying structure)
I'd say that a clear visible stretch and squash for this animation needs an animation on 1's (16 frames total or 8 per step) to make the forms flowing and that it adds up on impression without distracting too much.
It's possible to slightly shift the forms with 4 frames per step, although it rather will look like a change of proportions than an animation with shift (look at your sack again considering this)
However the current animation is too static in terms of vertical movement, so it might work out there.
The natural stretch and squash usually comes from a shift of weight or how the power if the body hits the ground is affecting it.
The bones stay static, the muscles shift their forms due to the movements but are somewhat solid, the fat on top always has a follow-through quality.
Means the bone structure of the feet hit the ground and after that (next frame) the fat gets the shock from the direction change and we have a squash (hope it's understandable what I mean there)
However we can break bones in drawing if we want to, an it might not even look off, if the timing and spacing is on spot.
Adding stretching and squashing (to walkcycles, which aren't fast movements) without a solid constructive foundation mostly leads to an unintended change of the volume of the masses.
For fast movements the mass preservation works considerable different.
But it's definitely worth to consider forms and construct them before considering deformation.
And then alter the solid foundation jus to the point where it breaks, or you want to break it deliberately in order to achieve another effect.
If you are going to break stuff make sure that it has enough frames, that the intended movement you want to describe to the viewer can be understood easily.
So for your sack and/or cat example this means, add either more frames to underline the animation or tone down the movement, to let it look more convincing.
