We have an 8 year old cocker spaniel dog (castrated) and are looking to buy a golden retriever pup.  I quite fancy a male but have been told that a bitch would be more likely to get on better with our spaniel. Any advice on this ?

The standard line of thought in a 2 dog household is male/female, male/male, female/female in order of placement.  That said, however, there are plenty of families that have 2 males or 2 females with no problems.  An older dog is more likely to accept a puppy of either sex.  Find the puppy that is best suited to your family, no matter the sex.