Rats love hammocks and rat tubes
. Fuzzbutts in the uk specialises in rat hammocks and hides (and the odd one for smaller furries) - you might get some ideas looking at theirs as well. There are lots of options to buy as well that are inexpensive to get you started. They love anything snuggly and Cody. Lovely you have Rosie and Bloom.
The snooze cubes are great - I have the hamster sized one. Good for lifting a hamster out of a cage.
Fuzzbutt Cage Comforts - Fabulous Furniture for your Fuzzies! Rat hammocks, chinchilla hammocks, small furry funky cage gear