It sounds like you're doing everything right. And support is what we're all about.
I did want to just let you know however that I had an amputation done on my girl when she had OS in the front leg. She was 12. She had a very very good 6 months before OS hit another leg.
And many greys have made it to 14, 15, even 16 yrs old. My own Onyx made it to 15.5. And I personally know of two that made it to 20 yrs and 2 months.
Unfortunately no matter what we do, they eventually leave us. Taking a huge piece of our hearts with them every single time.