Which part of Europe are you in? Zooplus sell hemp bedding in bulk which works out cheaper than Carefresh. You don't want to be putting something on the base to soak up odours - just use about 6" or more of substrate and a potty litter tray with chinchilla bathing sand in it. My cage stays clean and dry and our hammy pees in his potty
You have to put the potty in the right place for them to use it (ie where they have chosen to pee. If they pee in their house then give them a bigger house (eg cardboard shoe box) and put the potty inside the house (ie pop the house over current nesting area).