comments:
Mattturley posted on r/catadvice6d
I can’t search Amazon UK, but adjustable window screens are very common in the US - they slide to fit the window and are held in place with by fitting inside the frame of the windows and the weight of the window being pulled down on it. Since I assume this is a rental you probably can’t also add screws that some have to more permanently install them. These are not expensive in the US - far cheaper than a cage would be. This is the type of thing I mean - here is a 2 pack for 25 dollars US. Frost King 2AWS1045 WB Marvin Adjustable Window Screen, 10in High x Fits 25-45in Wide (2-Pack) https://a.co/d/01cKKbKO