Tbh nothing fancy. Get him at least 2g, a heater is a must (do not pass it up, you simply cannot.), a bubbler is not needed in any way nor is a filter, really. If you filter the tank it cannot be a strong one or the fish's tail will be ripped right off in a small tank. If you get one, put pre-filter sponge over the intake and watch that it won't knock the fish around and blow out its fins.
I've kept bettas for years- The ones who have temp. homes usually get a QT type tank, heater and thermometer, no gravel (what's the sense?), and some sort of decor which is not sharp in any way; silken plants or live are best. If you're getting an uncycled temp. tank, just use floaters if you can get/have them: frogbit, duckweed, water lettuce, etc. I would argue your water should not be room temp- especially if you're in winter where you are. Your barely 70'F water is too cold for this type of fish; opt for tap water around the same that you removed and replace with that. With a heater aim for 75-8'F, constant. I would never leave my splendens tanks to be at the mercy of my house's temp. fluxes in winter, or any other season.
Change the water halfsies each week and up to a full change once a week. It depends very heavily on your tank size. Test the water and check it, no sense in mucking around with it. Make sure the fish is properly acclimated each change and you're set.
Be very VERY careful when you unbox your fish- there is a good and bad way of going about it! Stressed out bettas who are poorly unboxed often bite up their fins and ruin that beautiful form you wanted. Open in a dark room, check to see if its alive, gradually re-introduce to light, then a looonnngg acclimation.