We had a great time at Casa Cosi, the flat is clean, very spacious and the location is central, in the heart of the gothic quarter on a very pleasant street. Plenty of towels were provided, kitchen is adequately equipped and there's a very dinky little balcony. About 20mn walk to the beach, 15 to the marina and 10 to the city centre.
As other guests said, neighbours won't tolerate any noise at all so careful with that.
I would recommend 100%, go for it!