Most King Charles Spaniels I've dealt with professionally have been real low key, lovable, great personality and easily trained. If you can't tell, I love this breed, except they have a very high incidence of heart problems sometimes starting at a pretty young age. If you find a line where this is not a problem, go for it. I think they are much like miniature retrievers. There are great rescues all over the US where you should be able to find an individual that fits your situation no matter what breed you decide on.
Doug, DVM