As the OP I want to thank everyone for the comments. I feel I have the info I need and will pick up some spray just in case.
After some research I have found the likelihood of a bear attack in Yellowstone is remote.
Since 1979, more than 118 million people visited Yellowstone National Park. During this period, 44 people were injured by bears in the park, according to park numbers. You’re just as likely to be zapped by lightening or drown in a boiling-hot thermal pool. There have only been eight reported deaths since the park opened 142 years ago.
I will not be hiking in remote areas, and in fact will probably be only in populated scenic areas. It sounds like I have a higher probability of being injured in a vehicle wreck on my way there!