I would add:
a down packable jacket, probably a vest for the possibly warmer weather you describe. uniqlo for value and cut or tog 24 for quality, warmth and performance (and the fact they used to do one that ¹packs into its own pocket not a separate bag). Personally I'd take both because they are both so small and handy, especially in airports (pillow anyone)(night time shuttle bus transfers) and airplanes.
A genuine performance waterproof pac a mac (eg Peter storm, mountain warehouse, tog 24). If you want to be a bit more stylish I'd grab a uniqlo trench (no hood) or mac but they don't pack so small or neatly into a pocket/bag. Should be Roomy so you can wear it over hoodie and/or down jacket as required. Between a hoodie, down jacket and water proof you Will cover pretty much every weather/temperature combo down to 11°c ish. Colder if you include thermals wooly hat gloves, but I'm thinking from your description you don't need that cold
If you have space: 1-2 extra short sleeve top/t-shirt, 1 (maybe 2 extra bottom half), and one dress or outfit that can be used if you want something smart. Work on the basis for longer haul you want 5 tops (vest tops pack so small they don't count), 5 bottoms, 3 jumpers (one zip up, one fleece one smarter) one "smarter" outfit.
Smart outfit can be included in the above if seperates.
I'd also consider taking some proper walking boots depending what activities you'll be needing. Swimming costume?
I'd pick a zip up hoodie/fleece for the airplane so you can just undo the zip for those in between temperature times or when you just can't be bothered taking it all the way off or your hot but your shoulders are cold.
Take a regular water bottle AND a large 2l water bottle to fill after security (althoughare they allowing water through these days. I used to have a Fantastic hydroflask(??? I think)l foldable one, although with hindsight any old bottle would have done.
Foldable holdall or backpack (depending on if your handluggage double as a backpack). Surprisingly handy. From putting coats in one bag at cloakrooms, to shopping, to swimming bags, to extra bags coming home. Since always packing at least one (even small hand luggage only) there hasn't been a holiday I haven't made use of it!!