for heavy books, it would be better to choose shelving made from solid wood. the particleboard bookcases such as the billy or bonde system tend to sag under weight. as for solid wood bookcases, you do quite a few choices, though colour wise, you're not so lucky. the norrebo (pic) in solid birch is a modular shelving system that lets you cover as much space as you want but the colour is not a great match. or you can also try the leksvik or ivar, which you could stain to match your desk.