Holiday with my sister July/August

[Fallulah]

Looking for ideas please. Definitely want a beach or a hotel with a pool. Definitely want good food, relaxation, people watching but also things to do (sites of interest, things to photograph, not clubbing). One of us us a teacher so we can only go at the most expensive time.
My sister celebrates a big birthday during the time we've pencilled in to go away. TBH I'm not sure how she's feeling about it so the opportunity to do something a bit memorable would be good too.

All the deals seem to be in Turkey but we're not keen. I like the sound of Croatia, Sorento, Portugal but don't know much about them. Apart from family holidays in Europe (lovely memories of Canvas Holidays but I want more luxury this time), walking in Switzerland and a trip to New York I'm not very well travelled. Did go to Costa Brava with an ex Boyfriend but found it a bit tacky.

Recommendations gratefully accepted!

No real beach in Sorrento.

Lake Garda is fab no beach but bigger hotels eg Hotel Poiano have massive pools etc. lots to see and do in the vicinity. Could do a day trip to Venice or opera in Verona for her big day?

I went to Croatia last year with my friend. It was a lovely relaxing break without kids and DHs.

We stayed on the outskirts of Dubrovnik - in the Lapad area. We generally lazed by the pool during the day - or took boat trips to the some of the small islands around.

There are certainly a lot of sights worth seeing there - so you can do a bit of culture then relax and enjoy the sunshine.

I was there at the end of May - and the temperatures were just starting to warm up - I believe it's pretty hot in July/August.

People were really nice. Food and drink quite reasonably priced (apart from the tourist restaurants)

No sandy beaches though. But the waters are crystal clear and there are often ladders for you to get into the sea.

Skiathos
Venice
Rome
Rhodes