Coughing in cats can
be a sign of asthma (I'm not saying that's what Tommie has, just something to consider). Here's a couple links to check out: http://www.felineasthma.org/moore.htm
As far as diet for kidney cats, the most important thing is wet food. What does Tommie eat now?
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler