Cool! Welcome to the forum. A lot of users suggest using Prime as a water conditioner by the way - you need very few droplets for your water and it saves you money in the long run.
Just make sure not to get anything like Ph stabilizers (Ph up/down), anything with "beneficial bacteria" in it, and stray away from Melafix/bettafix if your betta comes down with an illness!
If you want, along with purchasing your water conditioner (which should eliminate chlorine/chloramines), you can purchase something that helps eliminate stress...I prefer Kordon Fish Protect - it lowers stress level, gives vitamins, helps damaged fins, and eliminates heavy metals from the water. However, I think prime eliminates chlorine, chloramines, and heavy metals, so getting a "stress coat" supplement is up to you.
Since your tank is filtered, did you properly cycle your tank before adding your fish? If you didn't, the spike in nitrates from the new carbon filter can actually poison your fish to death...there's a lot of information on the forums on how to cycle a tank if you are unsure.