You should try tonic syrups. I love them as you can adjust the water:syrup ratio to your taste, and mix and match syrups and waters. My impression (correct or not) is also that there's more tonic syrups out there than bottled tonic water, so a lot of choice (at least last time I looked). Finally, the syrup concentrates take up a lot less space in the refrigerator.

The only tricky part for me was figuring out what ratio of water:syrup to go with for any given brand, but that isn't too difficult.

I've thought about making my own syrup, as I'm a lifelong tonic water fan, and make a lot of other things myself, but haven't wanted to mess with it.

There's relatively dry tonics on the market now too, but nothing will get you to quite the same place as the syrups.