It sounds like you may wanna give oat milk a shot.
Since you seem particular about what contents you want in it as well as what general location you wanna buy it in, I will suggest making it yourself, as it is quick, easy, and cheap to do so. Not to mention, you will end up with a product consisting entirely of water and oats (+whatever optional sweetener you may wanna add).
It takes mere minutes of effort:
- 1 cup rolled oats (100 g)
- 3-4 cups water (750 ml – 1 l),
depending on how thick you like your milk
- Soak the oats in water for at least 30 minutes. We usually soak them
overnight, but it’s not necessary.
- Drain the oats and wash them (discard the soaking water).
- Blend the oats with 3 to 4 cups of clean water (750 ml to 1 liter).
- Strain the milk using a cheesecloth, a strainer, a napkin or a nut
- Store in a sealed container in the fridge for up to 5 days.
The above guide is taken from the first result on Google for "How to make oat milk". The article contains a few more tips worth reading. Substitute with any other recipe if you'd like, this is merely a suggestion.