Welcome to YT! I know you want to find the perfect pup, but just be aware, that no reputable breeder purposely breeds mixed breed dogs. Reputable breeders only breed to better the breed. There is no betterment in mixing breeds. You will not know how it will eventually end up looking. Many disreputable breeders will call these dogs "designer" dogs and charge as much or even more for them than a purebred. That said, mixed breed dogs can be easily found in shelters or rescues. Personally, I don't understand paying more than a few hundred dollars for a mixed breed pup. I'm not talking down to people who own mixed breeds, they are cuties too, but there is no reason for the breeders to charge that much for them other than the demand for "designer dogs".
PS, I know you said you don't want to support a mill, that's very good!
Please be aware, if you don't already know this, that buying a pup from a petstore (or anything from a store that sells dogs or cats) is supporting a puppymill.