Careful with coral decorations. A lot of them have sharp edges that will rip up a Betta's fins
There are plenty of fake corals you can buy along with fake anemone. If I ever buy another tank(which I know I probably will haha) I might go for a salt-water look for a Betta XD That or I am buying a 5 gallon tank and getting some dracerna(lucky bamboo).
This website has plenty of high quality coral-like docrations along with silk salt water styled fake plants