Things that helped me transition in the first week:
- I made my own plain carbonated soda stream water and then added a splash of no sugar added fruit juice
- Passionfruit or Berry flavored LaCroix is probably the most palatable to people who are used to drinking soda
- I also made my own fruit infused iced tea by brewing the tea, chilling it, and then tossing in an assortment of berries. Black tea has a good bit of caffeine in it too so you get that boost you're used to.