I do not know of any other breeds with the same personality but 10-15 pounds heavier (I assume that's what you mean by a bit bigger) suggest you find a mix breed/mutt. There are a lot of dogs in shelters right now (the housing crisis has forced a lot of people to give up their well trained, well loved pets). If you e-mail you local shelters, ASPCA, and rescue organizations with a description and a picture you'll probably be able to find a King Charles that is large for the breed or a mix of a King Charles and another dog that is slightly larger.
PS- Not to bash other people but Cocker Spaniels do not have the same personality at all - they're over bred (lot of inbreeding) and tend to be more aggressive because of it. If you do decided to go with the breed be sure to get a 1 year+ old dog, not a 5 month old puppy whose personality is not developed yet.