I'm so sorry for your loss! I had to put my little girl (my ~200lbs. Mastiff) to sleep in November, and it was so very difficult to do. Not sure if it made it worse or helped to deal with it, but shortly afterwards I heard Passenger's latest song "Let Her Go" on the radio, and it struck such a chord with me and my loss. Even now if I hear that song and I'm not in the best mood, I'll remember my sweet Joni and may even get a little choked up.
But for Christmas, my best friend and I went out to a local Paws and Claws rescue and I got another little girl to cherish. I know she'll never replace Joni, esp. considering how much more (hyper)active she is contrasted to Joni, but I also know I'll come to love her just as much.
I wish you and your family all the best. It does get easier as time goes on, but it still hurts to lose such a great family member!