Okay so, the first "step" of fixing up and modifying my new Pikachu suit is complete, be converting the floppy slipper-things that came with it into actual "boots" that look more like the ones that that Chiitan for example wears, only yellow instead of beige.
To thicken up the "foot" part, I just shoved a pair of Eevee slippers I already had (seen here: http://fav.me/d8nq5al) inside them, and then made the "leg" part from fleece fabric stitched by hand and some bed foam inside to make them soft and lightweight but hold their shape. This entire process took two whole days. XD
Unboxing video: https://www.youtube.com/watch?v=ZRyJT6f4kTg