You don’t need a variable speed pump for the well. The well is a low producer, so you need a regular small submersible pump and a Dole valve to limit the flow to the production rate of the well. Then a float switch in the cistern will control that pump.
I also like a submersible in the cistern instead of a jet pump, but either will work. With three baths you need about 15 GPM at 50 PSI to handle peak demands. Then a CSV would let it run all three showers at the same time or make it work like a smaller pump, even down to 1 GPM, when that is all the water you are using.
The CSV will do the same thing as the variable speed pump. The CSV is just simpler, less expensive, and longer lasting than variable speed pumps. If you want to check up on that variable speed pump they are trying to sell you, just Google “CU301”. That is the controller for that variable speed pump, and you need to know how it has worked for others.