I just read that you lost Sophie a few days ago. I'm really sorry to read that, and very much understand what you're going through. As a dog rescuer I deal with a lot of dogs, some of which are old or ill. Even the ones I've known for a relatively short time are very difficult to lose. I still get choked up looking at pictures of dogs that I had decades ago. Each one takes a piece of your heart.
As for getting another dog, you stated your age as a possible problem. You probably aren't ready for another one yet, but when you are don't completely despair.
I don't know your family situation, but if you have other dog lovers in the family you might be able to make arrangements in advance for where the dog would go if you could no longer care for it. In reality, people of ALL ages never really know that they'll be healthy for the life of a pet and SHOULD make such arrangements. You can even make arrangements in your will, as we are doing, in order to ensure that funds are available to whomever takes your dog. In our case, we know where all four of our dogs and all four of our cats would go if something happened to us (not all to the same place). I'm called to rescue dogs that family doesn't want when someone goes into a nursing home or dies, and I'm sensitive to that.
Another thing to consider is adopting an older dog. The energy level is more manageable, the likelihood that the dog will outlive your active years is less, and the older ones are MUCH more in need of adoptive homes. Once one of the dogs we have in rescue turns 3 years old we know there's a good chance it will never be adopted. Everyone wants a young one, even though the young ones are a lot more hassle.
I hope this helps.
Rescuing Great Danes and hounds