There are a few good options in Oia. That is the best location on the island (the beaches on Santorini are not a draw, though the black beach is interesting to see). From the hotels in Oia the walk to town is flat and not far. The hotels themselves will have steps, most are set so that they sprawl a bit down the side of the cliff. Yet, if you email the property I am sure they can assign you a room on the main level, so to speak, near to the entry. Have fun. The view of the Caldera in Santorini is simply outstanding.