Our walking jackets are all cotton with Velcro. The Velcro is a bit of a problem with the Pixie Bob as he has both a belly pooch and long shaggy belly fur. No issues with the Velcro and a SV.
Ours are from Mynwood in the UK (about $20). What is nice about the Mynwoods is that they are custom made to your measurements. Knowing that my kittens would grow, I told her current sizes and breed of cat and she made them a bit bigger. She also has breeder-packs that consist of 5 kitten-sized ones. Does anyone know of kitten-sized ones in the USA? Our first jacket was given to us by our PB breeder and it was called "City-kitty" but I was never able to find them. Our breeder had bought it at a cat show.
My advice would be to buy a kitten-sized one now knowing that you will need a cat-sized one within 3 or 4 months.
I've been through so many different harnesses it's insane. I had Mynwood one for my Ragdoll early on, as well as "City-kitty," at least I think that was the one (or was it Kitty Holster?), I can't seem to find it again. Didn't like the "City-kitty" at all as it didn't fit properly on any of my 3 cats of various body shapes/sizes, Mynwood was good but the construction on the Joycatz was better IMO, and for Duma I do like the windbreaker material.
I do agree about the long shaggy belly fur issue, Desi has that, and it is a PITA but as long as I keep the velcro clean it works. Desi is not allowed to get any shaggier, fatter, or fuzzier. I never had a fur issue with Dante who also has long hair, but not the shaggy fuzzy kind.
The only true kitten one I've ever seen was from Petco and it's not an actually functional harness. But in my experience (leash training 3 kittens), the kittens don't walk well on harnesses anyway, and it's more to get them used to wearing the harness indoors, and maybe having a leash attached. I remember posting here about using a ferret harness for Duma, that lasted a few weeks after the kitten harness, then we were on to Puppia, and then finally Joykatz. I also have a nice one from Hyendry that we have for special occasions and/or when he gets a little bigger. The fact of the matter is that kittens grow, and you have to periodically buy new harnesses in the first months, and then again around 1.5 years. One of the harnesses I had at one point was supposed to transition from kitten to adult (I don't recall offhand but will post if I rec, but that didn't work so well, like Rafiki says a good fit is really important.