I have my bettas always in gravil, but thats only cause it's easier for clean up and ALOT more colorful. The betta just cares to have it nicly filtered, no other fish in such a size, no snails, and no flakes o_o Hikarie Betta biogold is perfict for a two gal betta. As to the planted, my betta lived 5 months without anything but a big dragon wing in the centure of the aquarium ^_^ So it's mainly what you like and what may look good with them, just be sure to have a dark plant for him/her to hide under when it's to bright. But for easy veiwing of your Betta, I suggest keeping them less clustered in fake plants and alot of green. It'll make the betta pop like no tomorrow and look even more beautiful!! *-*. Just keep a eye on algie, cause in a 2 gale the lights naturaly grow algie X_X, to warm and great for bettas. But thje algie will thrive if you get a porus plant, so if you could stick with a slick fake plant =D you'll have a happy clean, and relaxed betta with no worries ^_^.Just dont put yout hand in there and the plants when he/she is in it ! They freek out horibly and dont recover for days ...
And as the above said, a undergravil filter comes with filter stones and are some of the most perfict filter for your bettas, the good healthy bacteria will clean most of what poop they do right out and though you still have to change water, with a under gravil filter as long as you change it once every water change, it should be okay... By any chance did you get a Hawakey Top Fin version 9 1.66 gal starter kit that came with the tank =D You sound like you have the same exact set up as my bettas do! However in this case, I am STRONGLY againced useing sand with your betta, it will kill the filter and most likly clog the porus holes and leave you with returning the tank to the suspected petshop =/....And if you have fake plants in there, get another inch of gravil /rock in with it so that it isint resting derectly on top of the undergravil filter so you will have a easier filtration ^^.