I got a seltzer bottle.
Yeah, it's slightly acidic, but you're basically looking at water with bubbles in it. Buying CO2 chargers in bulk online makes it relatively cheap (local boutique market sells chargers at $1 each; online can find for 50c each or less).
Now… the exotic part. You can make your own flavor syrups if you want (ginger syrup? drink ginger soda til burp.) A dash of lemon juice. Splash of seltzer with whisky.
Before you splurge on Sodastream (hint: Don't; it's not cheaper than premix), look at a seltzer bottle.
If you really are drinking metric buttloads of whatever and need something with flavor, look at a postmix system and juice syrups for it. Not sure if a gun or a pedestal makes more sense for you, but obviously if you get a carbonated postmix system, you'll be back to drinking soda by the gallon and catching the diabeetus and losing your teeth.