Cats like routine, but even they can get bored with the same old thing every day, just like us. It really can be a challenge to try and keep a cat active and entertained, especially an older one. The key is enrichment. It helps if you can find creative ways to mix up their environment and give them new things to explore. This can be easier, and cheaper, than it sounds. A new box with holes cut in the side or a paper bag from the market can help. It's not only the new "place" - it's also the new smells that come along with it. Even making a play fort from a blanket over a couple of chairs can change things up enough to make them interesting for them.
When you come home, be sure to let your cat smell your hands if they’re at all interested. The scents left on your hands from your day tell a story and most cats very much enjoy the new scents from the outside world. Think about ways that you can share the smells you bring into your home.
I leave soft music on all day for my cats. I had one who was over-grooming and that stopped when I started playing music. My cats are both very fond of soft harp music like this: https://youtu.be/dCvEgqePl84
I've also had great luck playing live streaming nature cams for cats. Here’s one my cat like to watch: https://www.youtube.com/live/F1Q7iN_RWUs
None of this addresses activity, of course, at least not directly. When cats are more stimulated by their environment, I've found that they become more interested in playing. The way you play can affect their interest as well. The toy should behave like prey and it's better if the toy is moving away from the cat, not toward them. Many cats respond well to the "Da Bird" wand toy, but some don't. Each cat has a bit of pre-programmed preference for a particular kind of prey. If your cat doesn't have the "I want to kill and eat birds" gene, she won't be interested in feathers, but she might like stuffed toys. It takes some trial and error to determine.
If your cat will accept a harness, you could also take them outside for brief exploratory sessions. Cats enjoy exploring and, even though they’ll probably go about it very slowly, they would be likely to enjoy it.
As to adopting a new cat friend, it usually doesn't work well for cats above the age of four. I won't say it never works out, but it's risky. Older cats rarely take to new housemates.
Author: Tom Kirby, UW-AAB - cat behaviorist
I’m certified in applied animal behavior and have years of experience solving the specific problems faced by cat caregivers like you every day.
I’m here to help you and your feline friends live happier, healthier lives together.