How Much Mobility Can Be Expected After An Ankle Fusion Surgery?

I have severe osteoarthritis in my left ankle as identified by x-ray as well as symptoms. My MD tells me surgery is eminent... as I understand it, I will have 2 choices: ankle fusion or joint replacement. My orthopedist does fusion but not replacement. He says replacement is not usually successful.... I feel I need more information. How much mobility can I reasonably expect to have after fusion? How will I manage stairs, put on narrow leg slacks..... Has ankle replacement advanced to the point that I might expect reasonably good results? I am 75 years old, female, 5 5 tall and weigh 165 lbs. I have previously had both knees, both shoulders and my left hip replaced. All replacements I regard as successful and have occurred over the past 8 years.