Yeah upholstered cozy. Preferably something you can sit in and enjoy a good book.

Is your existing chair cozy enough? if so, I might move it to your space (if it would fit) and look for an accent chair, something colorful to go where the existing one is - that might not get used as often. The reason I'm suggesting that is it's difficult to shop for a cozy chair online, without being able to sit in it and we don't know what actual stores are available to you.

If that wouldn't work, would you like a small recliner? They make some really decent looking ones now (not sure if this would be your style on sale for 404 at Macy's):

Recliners are great if you don't have enough space for an ottoman. I have a mission style one and love it. Looks great up or down.

Another option to consider. Are you using that other chair in the other corner on the other side of the fireplace? Because if not, I'd switch it to the other side, get one of those groovy patterned upholstered ottomans for it (saw a bunch at World Market yesterday) and put a rocker in the space where that chair is now. I have a rocker in a small space next to my fireplace and like that I can easily move it in closer to the fireplace when it is on to warm up the room. It's also handy to move around to different locations when I have company. I mean I could be totally off, but it seems like no one would sit in that upholstered chair you have in there now unless they wanted to read or talk to people in the other seats, because it doesn't have a view of the TV or fireplace. But I could be totally wrong, just my .02 thoughts.

It would but I would have to shift the main couch over a little. I like your idea of an accent chair. Guess it doesn't need to be super comfy if it's in a corner on its own.

I would pull the chair in the corner out a little bit & add throw, lumbar pillow, floor lamp & small table to sit a drink & book. Then if you wanted to add something by the sofa-- it could be an accent chair- fun- maybe with open legs, no skirt. Doesn't have to be for comfort, but for color & whimsy when you need additional seating in the den.

Target & pier one have lots of these for not a big investment & usually on the smaller side, too.