Honestly, the age of the cat being introduced usually has very little baring on how well they will get on! If the kitten you introduce is not used to other cats (which it won't be) or your other cats get jealous then you could have fights on your hands regardless.

6 weeks is very very young for a kitten to be away from it's mother. Vets approve from that age because that is technically when a kitten can feed on it's own but it's emotional and physical nurturing takes place right up until 12 weeks and beyond. 9 weeks is generally considered to be a good release age by breeders on this forum.

You should try local rescues to see if they've had any unexpected kitten litters. I know that the RSPCA currently charge £75 for a kitten with kitten pack so you may need to pay a bit extra depending on the rescue you use.

At the moment we're well out of "kitten season" (usually May-August) when all the cats go crazy and get pregnant in the warm weather so rescues may be short on kittens. You never know though!

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Current foster from the Cinnamon Trust - 13yo Muffin the persian tortoiseshell kitty. And we're keeping her.