My instinct is always to go GREEN. lol.
Other people may think my obsession with heavy planting is a little OTT, but that's OK, I don't mind.
I look at all that expance of white sand and think that plant cover would make it more comfy for your betta, and also hide/disguise the dirt and algae when they start to accumulate, cos you know they will eventually. :)
So my suggestion is for a few low growing things in the foreground, like S.repens, and some tufty little crypts. I have had great success with planting just a couple of plants of dwarf sagitaria (sagittaria subulata) and then letting it run riot with its little runners, and forming a carpet.
As for the surface, yes betta love surface floating plants. As small bunch of watersprite or hornwort will spread and create a beautifully sheltered feel for your betta to feel at home. So long as you don't let them get too thick, they will still let enough light through for shade loving plants like your java and anubias. One other thing, if you are going for plants and sand, then you also need some plant fertiliser. Rooted plants either need nutrients in the substrate or they need root tabs buried in the substrate next to their roots. Sand does not contain any nutrients, so you will need to go with the root tabs. For non rooted plants (the floating ones, or unplanted anubias) you need the fertiliser to be in the water, not the soil. But that is really easy. A small measured dose of liquid fertiliser added alongside your water conditioner, whenever you do a water change only takes a second, but it transforms the look of your tank with plants that fill out, spread and flourish.
Hope that helps!
: mature setup; betta, purple rasboras, male guppies, amano and wood shrimp. Heavily planted.
22litre cube tank
: (Tagawa); betta, yellow dwarf shrimp. Pond snails and 1 assassin. Heavily planted.
Midnight in the 57litre tank
(Midnight) ember tetras, 1 amano, 1 ghost, 1 nerite, pond snails, 1 assassin, doing his thing. Heavily planted.
; honey gourami, cherry barbs, green neons, otocinclus, nerites, pond snails, amano. Heavily planted.