I know that feeling Paul !
I have three main bookcases - one large and two small - plus books stored on top of a chest of drawers, and have run out of space.
There are books resting horizontally on top of the vertically stored books, and books on the shelves of the bedside cabinets in both my bedrooms, as well as on another ratan shelf unit in my bedroom !
I have to seriously think before buying a book now, as I just don't have room for another book case. With the book storage, and the model display cabinets, the floor area in my house has reduced in size considerably - there are even cabinets on the stair landings !!
Oh look, another couple of books I'd like to get ...................