Hello,
Your Ikea Detolf is a very good option for your hamster to live in. The item doesn't come with a lid and you can't really find lids for your ikea detolf. Why not consider making your own DIY lid. Wood or plastic is a good option! Just simply measure the length of your cage for where you want to place the lid and just get a piece of plastic or wood and cut out the correct measurements. I would recommend wood for the lid due to it being more secure. Then drill holes to let air come in and out for your hamster to breathe.
For your cat, no matter what, you should not let your cat in your room without supervision. Cats will like to catch and kill mouses or any small rodents like Mouse, Hamsters and gerbils. Keep your hamster in a safe quiet place where it can adjust to the environment after you bring it home.
Good luck with your hamster!
