With Jessie, we used Benazepril (a heart drug used for kidneys), Renal Advanced (a probiotic), a multi-vitamin, Zantac (she was vomiting a lot), sub-q fluids (weekly at first, and increasing in frequency to daily at the end), and, when her appetite disappeared, anabolic steroids. She couldn't eat the usual kidney diet, but I found an alternative. When she decided not to eat that, my vet said I should feed her what she would eat. She was 13 when diagnosed and lasted over a year.
I have two more kidney dogs now, one grey and one non. Both are on Benazepril and Renal Advanced, one on Zantac and the other on steroids. Both are already being fed whatever they'll eat. Both are 15.
There are a lot of things you can try putting on your boy's food to help him eat, like grated cheese (parmesan), ground up beef liver, broth (be careful of the other ingredients), a bit of canned meat, and so on.
Dogs with kidney disease don't tend to last a long time, but some--like Jessie--do fairly well. It's good that you caught it early.