A friend of mine recently had this track with ball that entertain his loner cat for hours, check here http://www.petstreetmall.com/Turbo-Track/10134/4953/details.html
If the fever has few days now, he needs medical check up. Keep an eye on his temperature. A site said cat fever is commonly caused by
A bacterial, viral, or fungal infectionA tumorInjury from traumaCertain medicationsDiseases such as pancreatitis or lupus
Better to access your kitties last...
Felliway looks great! My Hannah loves the window and watch the people outside for hours. Maybe you should start finding out more things and stuffs that catch your kitties interest.