Cardboard boxes, paper bags, and sheets of paper are all better than anything I could buy my cat, haha. But all cats are different! He also loves to hunt birds (part of why he’s indoor only) so bird toys with birdsong were his favorites for years. I’d recommend not spending a lot until you “learn” your cat! And also, if you’re getting a kitten or a youngish kitty, they will be way more playful and like anything you throw at them!
Our cat is on several different meds and we go through a veterinary compounding pharmacy that is semi-local to us; they ship his meds. It is cheaper than the vet, and we don’t have to give a feisty cat 3 separate pills morning and night! Worth looking into that if it’s more than just the thyroid meds. It’s made life a lot easier.