Hi Emma, I remember the time I introduced two wire-haired jack russell pups into my (then) household of 10

cats, and this is what worked for me:
Admittedly the cats were used to a dog about the house; till recently I'd had an Alsatian, an old and ailing lass who'd slept all the time. The pups were going to be a real culture-shock!
I too thought puppies might be better; I'd tried to introduce a young rescue dog and it didn't work out; he just barked at the cats and the largest cat attacked him. However, since he'd been on death row and went on to a no-kill shelter, his stay with me, though another hiccup in his history, did save his life; he was a lovely dog. So I thought puppies might be more submissive and less threatening - and also more likely to back down if swatted by a cat; from the beginning they would have to learn 'no' about chasing/roughnecking and that the cats were boss, although every moment with the cats would be supervised.
The house I lived in then was an average end terrace, but we were lucky to have a huge dining room, a separate kitchen and a porch, so the kitchen became the 'kennel' when I wasn't about. The garden was secured, and to give the cats space, I made a makeshift low 'fence' a third of the way down that the cats could jump over and the puppies couldn't, so the cats could have some peace without being chased. The cats had the run of the rest of the house; the pups stayed in the dining room and kitchen. And no rules about cats NOT getting up on work-surfaces/tables to be out of the way of pups.
The pups had grown up with a cat too, and had learned to respect it, I think.
This is over 20 years ago and although it was hard work, all the housetraining, training, supervision etc, I don't remember any real trouble. Reactions were mixed, varying from disdain to a seal-pointed jack russell sharing the novel cereal and milk breakfast and curling up on the beanbag between two little hot water bottles! I had a ginger tom (I've almost always had a ginger tom!) and one of the pups would 'cuddle' him, her tail going nineteen to the dozen (condition of sale - those pups came with their tails!) He'd just purr.
However, this is just my story - and they are all different, so nothing's predictable.
Do hope you get your puppy though, and that the cats accept it - all the best
