Missing big sister

We had two dogs. One got sick and was put down by vet. Now the other dog is really missing his big sister. Anybody got any experience with replacing the dog to ease the other's loneliness?

I always replace a deceased dog as soon as it is practical. I usually choose the opposite sex to the surviving dog. Because I am now in my seventies, I prefer to adopt middle aged dogs, and allow them to initially meet on neutral territory. Sometimes it can take a week or so before they seem to be relaxed in each other's company, and food greed can be a source of friction in my breed. Perhaps I've been lucky, but I haven't had any lasting problems.

What age is your remaining dog ?

I've always replaced a deceased dog with another but i've tended to have 3