Planning a honeymoon to Greece – need recommendations

My husband and I are in the early stages of planning our trip and are looking for a low-key, relaxing but adventurous trip. I'd like it to be as authentic as possible and immersed in the culture. We don't drink or party anymore. I think we'd like to spend a few days in either Athens or Thessaloniki, a few days on a boat, and a few days on an island. Very open to hiking but I think we'd rather beach than hike for this trip.

I'm having a hard time finding a boat rental that's not a huge 10-person excursion. We're fine boating with others but I can't find anything online for a 2-4 person sailboat or something.

Is there any must visit places you've been to? Your favorite restaurant, beach, or market? Favorite bed and breakfast, airbnb, or cozy hotel? TYIA!!!