Ocracoke, NC. You can only get there by ferry. Love that little town!

I love Bald Head Island, NC. No bridge and no cars. You have to take a 20 min. ferry over. Almost completely residential-you have to rent a house. But beautiful, charming marina, 2 country clubs, 1 golf course, grocery store, etc. Not a ton of restaurants but you will have a house with a kitchen. Houses come with golf carts and everyone bikes or drives a golf cart. Very quiet. Not a ton of shopping but there are a hand full of high end, casual clothing stores.

I too look constantly for charming places like Seaside and Rosemary's Beach and they are hard to come but... Bald Head Island is a delightful, no cars, bike and golf carts only with beautiful beaches. Limited on restraunts but the harbor has a fun place Mojos, and a few other small places. Some boutiques and lovely art gallery Its quaint and quiet. Must book a ferry which is 10 min drive from Southport which in itself is old charming and fun with lots of shops and resaturants. Rent a house or condo (marsh views are awesome and lots of kayaking) for the week with access to The Shoals Club or at least the Pool. Tennis pretty golf course. Lucky me my friend owns a house and I go every summer. Bring a cooler of food and box of groceries- There is a wonderful market but prices like Tiffany's. Its also a turtle sanctuary with lots of learning and fun for children and Old Baldy Lighthouse. Total family vaca or respit from the world. Totally worth the effort all together. I've never cared much if it rained there all week which its only done once is 18 years you can go to the spa.
The Inn at Plametto Bluffs in Bluffton SC on the May River, 30 min from Hilton Head and Savannah is also charming, quiet, planned community but still there is nothing like Seaside or Rosemary Beach that I've yet to find in south of the Mason Dixon Line. I keep looking.. keep going back year after year.

I have never been to any of those places in Florida you mentioned but from your description I feel like you described my absolute favorite beach spot which is Fripp Island. It's in Beaufort SC, it's a private gated, little over 3 mile island and you can absolutely park your car for the whole stay. You can rent a golf cart to which you use to get around the whole island but with a lot of the house rentals golf carts and bikes usually come with your rental. There are also bike paths that lead you all over the island as well. There's no hotels it's all houses and one section is condos. There's about 5 pools, couple of restaraunts and a small food court (which they have the best quesadillas). There are 2 gift shops and a grocery store. The island is more known for its 2 golf courses but the beach is the best. Even in peak season there's still plenty of room on the beach. If you've seen Forest Gump they filmed the Vietnam scenes on this island and you can find pictures of him on set at the bonito boat house seafood restaurant on the island. Also there are things for kids as well like the small animal place (can't think of the name) but you can hold snakes and even a baby alligator. You will see all sorts of wildlife on the island. The deer are protected but some will walk right up to you. Also you will probably see at least one gator during your time there. I highly suggest traveling every rd on your golf cart even the dirt/sand ones at the end of one of them you will find a crabbing dock. This island is beautiful and I don't think there's an island out there that can compare to this one. It's quiet and serene. Im sure there is more I forgot to mention but I highly recommend this island.
PS
If your a fan of Forest Gump there's a place in the town of Beaufort called the chocolate tree. It's where his box of chocolates came from and they have so much to choose from, they are amazing!

I'll throw out Edisto Beach. Park and bike, walk, a few restaurants, one grocery store, and if you can't relax there, then you have a problem.

Vero Beach, FL
 

Small, no tee shirt stores!, beautiful white sand beaches, great no chain restaurants, no buildings higher than four stories (well, one slipped through). Stay on the island, not the mainland.

A hidden gem in Florida is Port St. Joe; alas on the gulf coast although you can enjoy the bay and the gulf all in one local.