This is my opinion.
Minimum 2 Gallon Tank ( I like the palpens)
25W heater eco/visitherm or Hagen Compact, all with thermostats, all these heaters are shorter in length and fit a small tank... you wont boil your fish !!!
Digital thermometer which you just stick onto your tank about $1
70% water change if your tank is unfiltered, once a week, buy dechlorinator such as "Fresh Start" and add required dose, if you have hot water put a bit in and mix with cold water, check with your thermometer so that your fresh water is about the same temp as the water in the tank.
A Gravel Vac with a siphon and a mesh sock.
Low lighting potted plant or floating plants such as Java Moss, Java Fern or Riccia, bettas nestle in them and go to sleep or lie on the leaves, plants add to the quality of water introducing oxygen. If you dont want to get real plants, then get silk plants, NOT plastic plants.
Feed your betta every other day, this helps to keep the tank clean (the more you feed the more waste your betta produces) I feed mine Hikari Micro Pellets a good pinch full, and once or twice a week mosquito lavae/bloodworms or brine shrimp just to give variation to its diet.
Optional 2-3 cories, they are bottom feeders and help to keep the tank clean too and also are tankmates to your betta, if you feel he is lonely.
Hope this helps some