I also have a "BIG" cavalier. He is 10 months and 18lbs. Very lean, just tall and long. I bought him from a respected breeder, and told him I was looking for a bigger pup for my 12 year old son. The breeder delivered! I'm hoping that he stops growing soon though, as he just fits in his bed and crate! I would talk to a breeder and see what you learn. Definitely would do that before tryign a cross-breed. Good luck!