I agree the Java Fern would be good here. This plant attaches to wood or rock (the rhizome must not be buried in the substrate) so it is easy to move within the tank (if that is what you meant). Moving it to another tank usually present little problem, though I have found that like most plants this can slow it for a time, depending. It may be the light more than the water that does this. If the "moving" was meant to be moving the entire tank home or something, then this shuld cause little if any problem for JF, much less than substrate-rooted plants.
Pygmy cories (Corydoras pygmaeus) are rather delicate fish. You must have sand, and they will be healthier in cooler water (say 75-76F max). They do not do well at warmer temperatures. I personally would not combine them with a Betta. The Betta might not take kindly to these little fish bumbling around, and they tend to stay in the upper water much more than many cories so this can be even more problematical. The Betta would likely be happier alone.
Byron.