The health of your cat depends on how much exercise and mental stimulation he gets. You can stimulate his mind with toys, treats, cat trees and more as well as his body by running and jumping.
Toys are the number one way for a cat owner to keep their cat happy. This is because cats are solitary animals who need stimulation by the owner in their daily activities. If you don't give your cat enough toys to act out their instincts they will find somewhere else to be stimulated. This could be your furniture or maybe their litter box.
Some toys will be for outdoor play while others will be for indoor play. Some are made of materials you and your cat might not like while others have a certain amount of noise and movement. The important things is you give them toys that are good and fun and don't over complicate things.
Another thing to consider when you have more than one cat is to make sure you have more than one litter box. Try to keep the litter box area low maintenance and keep the area clean as possible.