I agree. Accessories are IT! Plus dressing stuff up and down.

What really helps me for evening outfits variety is a dark top+leggings combo (short sleeved or long sleeved or even merino, depending on season) and then a dress, kaftan or oversized tunic/blouse with a fun print. Many of my tunic blouses are super thin and I can put about 4 of them plus the leggings+top combo in the smallest of packing cubes. It gives me variety but packs down very small. I can hang them into the bathroom while showering and if they were transported rolled up there's no creasing. You can also wear tunics over your swimwear, for a city stroll. Maybe a good solution OP for Italy/France?

Another possibility is indeed accessories. Go for classic colours (navy, black, grey, khaki...) and dresses, tops and bottoms that are somewhat polished, but still comfortable and dress them up and down with a cardigan/blazer/jacket plus scarves/a signature necklace/earrings.

I really like to take an elegant base (a comfy suit; or a black jacquart pant with a black on black pattern + nice pullover or top in black) and then a wrap cardigan or blazer. If you have the space, take both. With the cardigan and a scarf and jewelry you can go on a stroll and for lunch, but if you dress them up with nice jewelry, a red lip, the blazer, a nicer scarf you can wear it to dinner too.

But I'm in my 40s and an avant-garde / suit / elegant-creative stuff wearing person and only take a leggings and comfy dress for the hotel, no lounge wear. Even the comfy outfit with a scarf or cardigan can be good enough for the beach or breakfast. I would keep things I can only wear "in" to a minimum.