Is that back wall curved or just the way it looks in the pic? Can the bed go against the window wall so you enter to the feel of more open space? Windows are covered up anyway... I have boys around that age. One suggestion that helped us was to go with a twin xl bed for the length to accommodate growing boys. Full size doesn't have that length and queen can be too big. Use more of the wall space with higher shelving, etc. so the floor space feels more open. We put a lot of my 12 year old's "stuff" into the cubbies in a large IKEA Kallax unit against the wall. the depth is not that much but it is tall and long. My older son did a floor to ceiling open shelving look with IKEA Ivar. IKEA has a lot of ideas for storage in a small space - even if you didn't want the IKEA products themselves.

That is really tight -- a wall of furniture in front of the windows is a grim solution. Could some of his stuff go downstairs in a family room, say?

Otherwise, I'd consider a loft bed. That would give you room for a dresser and maybe a chair underneath, and you could leave the windows freed up. Second choice, replace one of the dressers with a storage bed that could hold all his non-clothing stuff...

Prepac Black Sonoma King Bookcase Platform Storage Bed · More Info

Prepac Espresso 12-Drawer Tall Platform Storage Bed - Double/ Full · More Info

Using existing furniture...

Maybe his closet could be better organized, so that one of the dressers could leave the room. More shelves, double hanging space, wire baskets. I like some of er612's suggestions.