I've always had more than one cat all my adult life, and for the last 30 years they've always been house cats, usually Siamese. Some have been same litter, sometimes not, sometimes totally different ages. Sometimes, with a dog too. Once we got 2 kittens for our elderly cat, who'd just lost her sister. They all got on fine. However if the age difference is big (over 7 years?) the kitten may not understand why the older cat doesn't want to play, so think about 2 kittens?!!
Currently my 2 (different ages) are snuggled together in front of a window. A few hours ago, one was snuggled into the dog.
To me, they are a little family, they ignore each other, they love each other, but there's always company there if they want it. So yes, I'd get a kitten, but I'd get another ragdoll - similar size, similar disposition