As @David White has pointed out, at low voltages the body's skin impedance when dry is very high. Therefore no matter how much current is available from the voltage source, only a small amount of current will flow through the body due to its high skin impedance per Ohm's law. So a 12 volt lead acid battery which has plenty of amps available will not cause an electric shock. (It could certainly cause burns if it contacts metal in contact with the skin).
The National Electrical Code (NEC) generally considers 60 Hz ac rms voltages that are less than 30 vrms at the output of an isolating transformer to be low risk with respect to electric shock under dry contact conditions. For this reason circuits connected to the secondary of a step down isolating transformer with output voltage less than 30 vrms is generally considered low risk of electric shock. These transformers, if they also comply with output current/power limits for fire considerations, are sometimes referred to as NEC Class 2 transformers.
When the voltage gets higher, or the skin gets wet, the skin impedance falls. Now the limiting factor is how much current is available from the voltage source. That will depend on the source impedance. For ac 60 Hz rms current the threshold of startle reaction is generally considered to be in the range of 0.5-5.0 mA. GFCI's are designed to trip at nominal 5 mA. From 5-10 mA the inability to let go becomes a possibility, depending on whether a child or adult. As the current through the body goes beyond 10-20 mA the the risk of ventricular fibrillation, and at very high currents, cardiac arrest, becomes greater.
There are many other factors involved in the risk of electric shock, too many to go into here. For example, at higher frequencies the skin impedance also drops (due to its capacitance). On the other hand, at higher frequencies a higher current is needed to produce the same physiological effect.
Various safety standards, in the US and International, publish voltage and current limits to reduce the risk of electric shock. They should be consulted.
With regard to your following statement:
high V low A electricity is transformed into low V high A through a step down transformer for safer use in homes
If you are talking about the high voltage outside the home being stepped down to 120/240 vac by the utility transformer on the pole or under ground, the output voltages from those transformers do pose a risk of electric shock.
If, on the other hand, you are talking about step down transformers that step 120 vac down to 30 vac or less, such as transformers used in electronic equipment, or bell ringing transformers used within walls to power door bells, as I described above, then these transformers do reduce the risk of electric shock because the body impedance is very high at low voltage.
With regard to you comment to @David White, it doesn’t matter how much current is available from the step down transformer if the body impedance won’t allow it to flow. It is the current that actually flows in the body that determines the risk of electric shock.
Hope this helps.