I use either of the following three, paper-based bedding for my hamster, and I use tissue for their nesting material. I usually wait to stock up on any of these three items when they are on sale and then buy them in bulk to save money, lol. These are the regular, non-sale prices for these items, but I can often purchase them for cheaper during the holidays, promotion days, etc. I am not sure if you can get any of these in Switzerland, but hopefully this will help you compare prices and see what other members have found working well for their hams. Good luck. I hope that you will find something that works well for you, your budget, your ham, and your mother's allergies.
1. Kaytee Clean and Cozy 28.3 L bag expands to approximately 85.0 L costing $18.99 U.S.D. from Chewy.com
2. Eco-Bedding 4.5 lbs. bag expands to a maximum of 125.0 lbs. costing $16.99 U.S.D. from PetSupermarket
3. CareFresh Complete Natural Paper Bedding 25.7 L expands to a maximum of 60 L costing $14.24 U.S.D. from Chewy.com