I am so very sorry.... I know that the loss of precious little LuLu has left a huge hole in your heart. It sounds like you are doing all of the right things to all yourself and those who love LuLu the opportunity to grieve and say goodbye.
Only you will know when it is time to allow another Yorkie into your home. I can promise you that although there will never ever be another LuLu just like you said -- a new pups will help fill the hole in your heart. Nothing helps the healing process more than tears and laughter. Good luck to you -- sending hugs
