Water Conditioner I use is Prime (Best in my opinion a bit spendy but it lasts for a while. Cost for a small bottle is about 6.99, Big Bottle 8.99. Bought at Petco.) Pour a couple drops into tank after every water change.
I also keep my bettas in 2.5 gallon glass tanks ($14 at Petsmart over where I live). (I have 4 of these guys.) Except for one that is in a 1.77 but he's a small male (wasn't power grown) eventually I'll be switching him to a 2.5 glass tank.
I have at least 3 SILK plants (never use plastic it can rip their fins apart) in the tank with plenty of silk leaves on the plant so it provides a good hiding spot for him. (They live in Thailands Rice Patty Fields so it's heavily planted as you can imagine.) If you want to get into keeping live plants. Like Java Moss do some research. Live plants are even better for these guys but silk plants are good as well. (Petsmart has a 3 pack. 2 - 6" plants, 1 - 8" plant.)
I use marineland 10 watt heater ($21 Petsmart) for these tanks. It's submersiable and auto shuts off when the water reaches temp. 78 Degrees. (They should be kept at 78-80. 82 for when the fish is sick.) The brand is very high quality.
Gravel/Marble is optional but not a must to have in tank. Some people say differently but it's up to you. It's nice to look at though ^.^. 3 Tanks of mine don't have gravel the 1.77 has marbles in the bottom.
As for food HBH Betta Bites, Top Fin Color Enhancing Betta Bites is what I use. Their happy as can be ^.^.
Anyways that's basically my full setup.
Oh yeah and when u do water changed float the betta in the cup you got from the pet store so he can get used to the water temperature. I do this for about 10 mins then pour some water out and fill in water from tank into cup (I pour about half the water out.) Do this twice. Let sit for 5 mins each then gently pour the little guy back into tank.
Anyways that's everything I do. If you'd like to see how my aquariums are setup I will gladly post pics from my 4 aquariums I own.