I'm curious, is there anyone else here who tried to introduce a harness to their cat? I did, and I have to say I found it much much easier than I thought. It probably depends largely on your cat's personality, but it might be easier than you think.
I decided to buy a (very) cheap harness because my cat is young and very active, he likes to play a lot and he constantly looks outside the window yowling. The area around my house is full of cars and dogs, though, and the garden is unfenced, so I couldn't let him out without a harness.
I made a horrible mistake as soon as I bought the harness: I tried immediately to put it on him. I hadn't even figured out exactly how to use it, but I was very eager to finally take him for a walk. After 2 minutes and uncountable scratches I went on the Internet for help.
I did exactly as the guides I found online said: start slowly, let the cat recognize that the harness is part of his environment and is harmless, use treats and so on. And it worked!
Mind you, he does not like being harnessed. He tolerates it. And another thing: it's not like walking a dog, your cat won't follow you, and if you stop him from going somewhere he will not change direction. He'll keep pulling. This might be only my cat, but it seems in line with their nature.
I suggest those with young cats to give it a try. It takes some time and patience, but it's wonderful to see him chewing on grass and chasing butterflies! I don't know how an older, indoors-only cat would react to being brought outside though. What do you think?