Those additional photos do give a lot of context. It's not a bad spot for a bookcase.

I don't especially love the cases you posted as shown (although they'd be fine when all booked up because they're pretty minimal) but I like how the open feet let the floor do its thing. Be sure they are deep enough for your books. This style bookcase makes it all about your books.

The antique one linked above is maybe a little less about the books. 😁

I love antique case goods so I know which way I'd go, but the clean look of the ones you picked out is pretty nice. The important thing is nooooo don't do built-ins over that floor and under that ceiling!