What is the best urinary tract struvite management cat food?

My cat has just had an operation to remove his penis and to create a new wee hole....due to severe crystals in his bladder and urethra. These crystals could not be removed by dissolving solution. I am now looking for the absolute best in cat food...to maintain his FLUTD, and prevent its return. We are very lucky to still have him. Its so confusing researching all the prescription diets...and some good advice would be most appreciated. Thanks in advance.