My aunt has a book of aquarium styles, not all were for bettas but you could betta proof them. these are the ones I like:
Hamster tubing was used to create a bunch of short interval ed tunnels for the fish to hide in with fun colored gravel and plants. Im thinking if you got the clear ghost knife fish tunnels they're short enough for bettas!
Zen: this one had bamboo bridges and white sand and rocks it was very pretty with a white background
Lights: These had those ceramic/glass lamp covers (how would you get one of these tank safe?!) that you can find at walmart and they were situated in the tank along with AQ proofed light bulbs and clear plastic bird ladders.
I definitely love the hamster tubing one but I may shoot for a zen when I have the funds.