Most waterways in NZ are not 22-26 deg. This is a country with mainly temperate climate. The problem is not usually temperature but light. There is a variety of Sag which does not not grow tall and only needs moderate light (will do better in good light) called Sagittaria microfolia. Otheres needing good light but remaining shortish would include Echinodorus quadricostatus, tenellus latifolius, tenellus tenellus, tenellus parvula. They all need pretty good light and a bit of calcium.