Finding space for your stuff is hard without adding on to your home or moving into a new one. However, many of us have at least some extra space hiding inside our walls.
Assuming your home is suitable, Installing shelves in between studs in your wall isn't as hard as it sounds. Home improvement blog The Family Handyman has step-by-step instructions on how to cut a hole in drywall and place a shelving frame in its place.
Built-In Shelves [The Family Handyman]