Help with planning Dec'24 to Feb'25 visit to Sevilla

My wife and I visited Spain for a couple of weeks over the Christmas & New Years holidays last year and we fell in love with Spain... especially Sevilla.

So we're planning to return for a couple of months next winter to get a feel for a possible long-term relocation. I'm hoping to find suggestions and help with a couple questions. Any tips for a first longer-stay visitor are also welcome, of course.

• Any recommendations for sites or contact to locate short-term housing from approx 9 Dec '24 through 3 Feb '25. Is Airbnb a good option or are there better local sites?
• We're questioning whether or not a heated flat is necessary. We don't normally heat our home and wondering how cold it might commonly get in an unheated flat. I'm guessing that there is little insulation in the exterior walls in the older structures but wouldn't mind being surprised to learn otherwise.

Thanks in advance for any tips.