I second the recommendation for the Mammoth Hotel. It's old but comfortable and the surroundings are unique, with the old Fort Yellowstone buildings and nearby terraced hot springs. It's also a mecca for herds of elk that sometimes surround the hotel! Riding stables are there, too. I also liked it for access to the Lamar Valley, a great area for wildlife, Tower Falls, and Mt. Washburn. We also spent a night at Grant Village but I liked Mammoth best.
One of the terraces at Mammoth:
Mama and her calf trotting across the grounds of Ft. Yellowstone at dusk.
After a Summer shower in Lamar Valley:
Hope you have a great trip.
Dick:)