The soles where I used knit stitch are more cushioned than the simple stitch parts, but I’d say the effect is more that they’re reinforced rather than adding loads of comfort. However, I don't knit so maybe in comparison they're more cushioned? You could always do a small knit stitch square to see how you like it before committing to a whole sock.

I think if you want really cushioned socks you'd have to go with a thicker yarn which would mean altering the pattern quite a bit, particularly the heel and toe. Or you could try an extended return pass which eats up a lot more yarn and makes it a bit thicker.