Don't you worry. There is no reason at all why domesticated cats can't live healthy happy lives indoors, it just takes a little bit more effort to keep them entertained is all.
One of the reasons indoor cats get kidney disease is probably age related more than anything else as indoor cats tend to live longer lives in general and so the incidence of illnesses like that increases. Also, you are probably more likely to notice urinary problems in indoor cats because they toilet indoors, I am sure many an outdoor cat has them, is just not so noticeable until later on. There are foods available to help, Cashie had a wee wee problem last year and so he gets a few Royal Canin Urinary bickies every day and it hasn't reoccured.
Vets are entitled to their opinions but they are not always right, we had a horrible incident down here in Kent where a vet shot a beautiful healthy fox just because he thought it might have killed his parent's cat. Sad about the cat but it was 19 years old and left out all night so I feel his parents had a responsibility to look after their geriatric cat, the fox, if it did kill the poor cat, was only doing what comes naturally.
You are damned whatever you do, if you let your cat out it can be run over, poisoned, stolen, killed, lost, shut in, abused by petty neighbours who don't like it in their garden, list is endless.... if you keep it in it might get bored. I know what I would rather have, I can always invent new games for my two.
Don't feel guilty, for every vet that says let them out there's a vet who says keep them in. If you have a dog, rabbit, goat, horse you don't let it wander about freely do you? they are enclosed even if outside. Same applies for cats I reckon.
Does Amber not get on with other cats? Is a shame as a little companion is always nice, My Cashie changed dramatically when we got Izzy, they are SO cute together. Was she an outdoor cat before? I have seen people take their cats out on harnesses, not sure if a good idea.. I had a harness, couldn't get it on the flaming cat though!
XXX