We've been to San Sebastian at least twice a year for 10 years and we have to say that this the most comfortable, cleanest, well equiped place we've been to!
The terrasse is just a total sun bath all day long, from breakfast to dinner, you dont have to worry about it. If too hot, you can always use the 2 large sunblinds. The location is perfect, not too central to avoid tourists and not too far from anything. If you cant walk (I am currently with a broken foot...) or just lazy at night, you can reach any part of the city using buses. The neiborhood is really nice and typical, all you need is there.
On top of that, our dog was welcome which is very unusual in Spain.
Bref, we had the perfect stay you are looking for, thank you so much Francisca and Tanya.