Some birds also have to be "taught" to play with and chew on toys. I don't know what the birds circumstances were before coming to live with you but if it is either a young bird or an older bird that has not had much experience with toys it may actually not know what to do with a toy! You can use a reward system to reward your bird with a treat or praise when it first "touches" a toy. Then move up to rewarding if it actually "mouthes" the toy. Then if it "plays" with the toy. If you get your bird to actually touch the toys, ring the bells etc and it still doesn't show much interest then it just doesn't want the toys and wants interaction instead. This does not mean don't provide toys but also don't worry if it doesn't show interest after showing and rewarding for knowing what the toys are for. Also make sure to try a large variety of toys, some with bells, some with rope, some wood, some plastic, some that move, some foot toys like balls with bells in them etc. If after having choices and "knowing" what they are for it is still not interested then at least you know you have tried.
As long as you are giving plenty of interaction to your cockatiel you shouldn't need to get it a companion. IF you are gone for extremely long periods or are not able to provide much time for it then a buddy might be an idea but you would have to have a separate cage for at least the first 30 days if not forever because there is no guarantee that your first one would get along with the next one.