I personally don't think you are being disloyal at all, we had our previous cocker Donald for nearly 16 years, we lost him in the November and George was born a month later in the December, he certainly did'nt replace Donald and i have never forgotten him
we found we just have more love to give to another one. Only you can decide what feels right for you, although this new little guy does sound as if he would fit into your household very well.
Good luck whatever you decide
Stephanie, George and Hamish xxx