I don't have personal experience with this myself, but breeders in Japan use 2 liter soft drink bottles. Cut the top part off where it starts to become narrow toward the lid, use a lighter to melt it a tiny bit around the cut edge so it is not sharp... And you are set to go.
You can put well over a liter in and the top is still too far away for jumping. They are also "free" and can be trashed if a fish is sick or dies.
They are shaped to be packed with the least space while being sturdy and holding the most liquid. The breeder I bought my pair from lines them up in a water filled styrofoam box with a heater in the middle to keep them all the same temp.
I have been saving and prepping all of mine to get ready for breeding.
--- Just looked and it seems like the 2 liter bottles in the US are much weaker and flimsier than the ones we have in Japan.
ETA: Pic of juvenile betta growing out in a bottle...