As both of you like beach, how about Bunaken in North Sulawesi (Indonesia)? It is famous for its clear water, perfect for diving and snorkling. The culture is very different to Bali's, so you get to see variety of cultures in one visit to SE Asia.
There should be a direct flight from Denpasar (Bali) to Manado (closest city to Bunaken), or transit through Surabaya. Make sure you also include domestic and budget airlines in your search.
Enjoy it.