Prayers that Henry will feel better soon. I had a Tortie cat named Jade that had kidney failure. She was diagnosed with it at the age of 18 when she was getting a dental and the bloodwork prior to that showed she had kidney issues. She went on to live for 4 more wonderful years. At first she was on K/D and she LOVED the dry version but wasn't too keen on the wet.
After a while she didn't want any of it and the vet said to make sure she was eating, even if it wasn't low protein. So she was on regular food for the last year or so.
The biggest impact on her disease was fluids. They really gave her quality of life. Before we started, she looked alot like Henry did in that photo you posted. She was dehydrated and her fur had that dehydrated look to it.
The techs showed me how to administer the fluids and let me practice a few times at the clinic and then sent me home with a bag of fluids. I swear, it is not that hard at all once you get the hang of it and it only takes 5-15 minutes, depending on what gauge needle you use and how many cc's of fluid you are giving.
I gave Jade 100 cc's once a week and she felt better within an hour of getting it. She would race up and down the carpeted stairwell and play. It made all the difference. Cats with kidney disease drink so much but they have trouble staying hydrated so providing extra fluids helps them feel so much better.
Plus, it isn't expensive. One bag of fluids lasted 10 weeks for Jade.