It's the shape of the seat top that got me. It's rounded and not flat.
At the simplest, remove the cover and shave the top down flat in the rider's area using a carving knife. Next, take a coarse sanding block and buff the foam smooth again before reinstalling the cover.
Tools needed: Heavy duty stapler, stainless steel staples, knife of your choosing, sanding block/paper.
Feeling adventurous? Buy a piece of 1/4" seat gel (eBay, etc...) and install that after you get the foam flat. There are videos on how to do that.
Done patiently, the seat will look stock and be a lot more comfortable.
The attached photo is of my bike's seat that has been flattened and had the gel added.