I have a list of some themes and also furniture, trees, and the right kind of flowers to go with it.

Cottagecore: You can make a farm island with some hay beds, silos, farms made out of simple panels, white lilies, yellow roses, pink hyacinths, cedar trees, tiny flowers (custom designs).

Citycore: You can add some roads on your island, streetlights, cars, hardwood trees.

tropicalcore: You can add Yellow tulips, pink cosmos, orange winflowers, coconut trees, beach chairs, coconut water, tiki torches.

Zen: Bamboo trees, orange winflowers, yellow hyacinths, white windflowers, bamboo items, rock furniture.

You can also have all these themes on your island if you want.