Sorry to hear of your dogs health...
We have had to put down several cats over the years and it is NEVER easy, but I am 100% certain it was the best thing on each occasion.
We have always had our vet make a house visit. The vet actually looks over the animal, asks a few questions and makes a practiced and professional opinion.
After each such evaluation the vet has agreed that prolonging the animals life would be inflicting suffering.
I have always been with the animal during the time to calm him/her and say good bye.
NOT easy, but I’m happy I did.
Since we live in the country I have buried all of these beloved creatures in our field in places they used to hunt or just hang out in. I plant a perennial on their grave and it’s nice to see the flowers come up in the spring.
Bless be to you in this difficult decision.
If you have any doubts a vet will give the best opinion. Go off his/her opinion and nobody can say you made the wrong call.