Find the breed of cat with ears and tail that best matches your aesthetic preferences, and fur the colour you want. Take young, healthy, robust specimens and inject the growth hormone directly into their circulatory system, in a large vein, not an extremity. Scale the dosage down, based on mass ratios, from what is effective on humans (this information is known to scientists, and can be accessed on journals. You'd have to pay for it, but that's a small price for salvation). Some cats will die. Adjust your dosage, and figure out a way to keep them alive. (Exercise and diet will be manipulated. Upon scaling the animal up, there will be issues. Maybe the circulatory system can't cope; if so, use steroid injections to strengthen the muscle. If the bones aren't keeping pace, add metal plates as extensions like we already do for humans in some surgeries. You get the idea. Fix the ♥♥♥♥♥♥♥ problems)