I know what you are going through. After my Father passed, his old dog became too ill and would have had to tolerate many operations for the rest of her days. Due to her age, we decided to put her down before her pain was too much to bear. I buried her in our garden.
Last month, I lost my cat of ten years suddenly and was devastated. I planted an oak tree on his place of rest. A week or two later I bought a briar pipe with a cat standing behind a tree as a remembrance. Lately a neighborhood stray has claimed me and usually appears when I go out to smoke, often with that pipe. I can finally take him to the vet this week to have him checked out so he can join us inside with our roomate's cats before the hardness of winter hits.
My pets have always reminded me of the fragility of life and helped me appreciate every moment for what it is. A fleeting chance at joy, contemplation, love....and someone to enjoy that moment with. I wish you and yours the best.
-Michael