Well you have picked an island full of good value resorts and private villas as well as some of the best hotels in the world for your honeymoon.
Three weeks is a long time for Bali so you should consider short trips moving to nearby islands.
It all depends on your budget. There are plenty of inexpensive family run places and very good value luxury-lite hotels. Take a look at wakaresorts if thats beyond your budget do a detailed search here and someone will direct you to a great honeymoon.