Do you have any bigger pictures?
So, I'm approaching this as Lucario translated into a onesie.
I get that to maintain the comfort of the onesie there's a few details you'll need to just do away with, like the spikes. But I do think there's a lot of detals missing that'll take this more from 'dog' to Lucario.
Starting with the hood, there's really not enough black. If you look at a back sprite of Lucario the upper half of its head is almost completely black. There's also a black strip that goes down the middle on the front of the head.
The. Uh. Puffy dreadlock-like parts should probably be puffier than what you have them. Bonus points, they'll be even more like pillows.
It could just be the picture, but the torso area should be a cream or yellow color rather than white.
The torso really doesn't need to be as long as you have it. It's taking away space that should be taken up by the blue of the leg.
It'd be beneficial to add a piece that represents the fur 'collar' around Lucario's neck. It doesn't need to be complex, just a flat piece of fabric cut into a 'spiky' design (Or a couple of flat layers if you're feeling fancy) that goes around where the hood connects to the torso.
There should be a thick black strip that delineates where the 'pants' start and the torso ends.
I almost didn't notice the black shoulder panels you included. I think they need to be bigger. Like, they should be going under the armpit region just a little bit.
Now here's where I go a bit overboard...
If you wanted to capture the Lucario look while feeling super comfortable I can think of a few modifications to the silhouette that, in theory (I've never worn pieces like this), that should capture Lucario's style without sacrificing comfort.
You could make the black shoulders puffy like
this (I'm thinking the middle one would be the most comfortable.)
You could do the blue portion of the legs as puffy shorts like
this.
You could then have the lower region of the 'pants' flare out to reflect how Lucario's feet get bigger.