A very exciting time ahead getting a new member of the family! Who doesn’t LOVE a Golden Retriever!? They are beautiful companions, so I can understand your desire to get this type of breed.
If you are wanting a smaller version of a Golden Retriever, you should consider a Nova Scotia Duck Tolling Retriever. They are a very intelligent, active, affectionate, medium-sized breed dogs that look very similar to a small version of a Golden Retriever.
When it comes to cross breeds it can be tricky to predict the size your puppy will grow to become, and whether the traits will be more one breed than the other, so this is something to consider. First cross puppies (F1) have something called hybrid figure, where they are less likely to demonstrate recessive genetic diseases and have biologically better traits due to their greater genetic diversity.
As you mention there certainly are different diseases that each breed (Golden retriever vs Poodle vs Cavalier King Charles Spaniel) can be more predisposed to. It is important that the breeder is screening for any genetic/heritable diseases relevant to the breed(s). Depending on the breed in question, this may include elbow/hip/spine scores of the parents and ideally grandparents of the litter, and DNA tests to check for other genetically linked diseases. Also, ask about the breeder’s policy for situations where a puppy from their litter ends up with a serious genetic disease later in life. Ideally go through registered breeders and always visit any prospective breeder’s premises to ensure the environment/diet/health care of the breeding dogs and pups is a desirable standard.
I hope this has been helpful for you. I hope you enjoy deciding which breed/cross-breed you would like to join your family. Make sure to send us a photo of the new addition to the family!
All the very best,