help alex find happiness again

i never thought i would have to ask for help in this way but i really need your help, my son, alex who is 6 years old and has ADHD has recently lost his best friend (our golden retriever dog).

they were so close and sophie (dog) really helped with his adhd and helped him learn responsibilities and they both got rid of excess energy on a daily basis which helped him sleep better at night and calm him down a bit more. they were never apart and it breaks my heart to see my child so upset everyday, he refuses to eat and does not sleep well at all. he always asks why his best friend died and where she is now and it kills me to have to explain it. my goals are to raise enough money to hopefully give my little boy his happiness back and get him a puppy golden retriever, i know it will never replaced what hes lost but i have never seen him so sad it breaks my heart :( i hope you can help me i known there is much more important causes i just really dont know what to do. thanks for looking