>> I am very sensitive to electricity
There is very few zappers taking this point into account. Most of them seek “MegaPower” and high voltages, when what works in a zapper is tiny currents and time exposure.
MZ3b is a zapper with a control on the output giving you as little as 2mA (adjustable constant current source). There are other hand-held zappers having too this rare feature (output control)
With a standard zapper, you should avoid if possible “super stabilized wave” circuits, because their high pass filter will give an inrush of current on every rise and fall time of their square wave.
Have you think of a little zapper as the MZ5? Its low voltage (5V) is well accepted by many people like you.
You can too use, with a standard zapper, tap water only (not salted) and 3 to 5 layers of wet paper, until your body stops complaining. As your immune system will gain control and be less on the defensive mode, you will be able to use more and more “high levels” of current.
>> I'm still waiting for somebody to create a zapper that has programmable frequencies. Not sure why somebody hasn't done that yet
A zapper works on a “large spectrum” of pathogens because it works with DC current, not frequency. Frequency effect is an additional bonus targetting a single pathogen, and requesting precision, and precision is expensive.
If only frequency interest you, you doesn’t need a zapper and its “DC offset”.
You have plenty of frequency generators able to work like a zapper with good precision. They are big and not cheap.
VariGamma is a programmable frequency zapper.. $586 on ToolsForHealing. Not cheap neither.
Now, what would be your (budget) choice : A 6 fixed frequencies, like the MZ6, a Frequency generator (usually not programmable) or a VariGamma?