There's hotels of all varieties within walking distance of the coast, whether you want beach resort type of visibility or, a cute harbor, San Sebastian has it. I've stayed a bit more inland so, a 20-min walk from the water's edge versus, open up my window and watch the waves type of location. For food options, no need to eat hotel food, San Sebastian is one of the great gastronomic food capitols of the world, from Michelin-stars to hidden gem counters, don't coup yourself up, indulge. What you won't have to do is drive, no need and no place to park so, leave it at hotel parking for a few days.
Harbor Area - right in the old town center, where all the lively pintxos bars are and next to the harbor and aquarium, can't get any more central
Lasala Palaza Hotel - We stayed next door and would like to return here on our next trip.
Sanse Bay Hotel- We stayed here on my second trip to Donostia, would recommend it to anyone
Ur-Alde- Much more basic than the previous two locations but, modern and 60-second walk to the shoreline
Parma Hotel- located in the old town but faces both the river and bay, great long view of the ocean shoreline
Playa de la Concha
Hotel de Londres- facing the picturesque scalloped beach and protected bay, within easy walk of old town. Likely a bit easier to negotiate with vehicle than those harbor locations.