Using Buffer Tank With Internal Coil To Preheat Incoming Water To Electric Water Heater.

I am told that the desuper heater circuit on a water to water geothermal heats water to the 120 degree area not hot enough for me. Therefore I am thinking I would like to have a 80 or 110 gallon buffer tank heated by the water to water geothermal with 1" fittings in and out that would allow the geothermal to heat water in the tank (as a buffer tank). Then I would like an internal coil in the buffer tank with 3/4" fittings that would have enough surface area to preheat water to the cold side of my domestic electric water heater as to allow it to top of the last 20 or 30 degrees. This would accomplish three things number one it would not require a geothermal unit with a desuper heater, it would greatly increase the amount of domestic hot water available and it would capture as much of the efficiency possible from the geothermal unit heating both domestic hot water and zone heat. My question is does anyone build a buffer tank with a coil to accomplish this? Most tanks are built as domestic hot water tanks that use the coil with 1" fittingsto be heated by a boiler to heat the domestic hot water which has 3/4" fittings.
Does anyone build such a tank? Heat Flo makes a stainless steel tank with stainless steel heat exchange coil but again it is designed to heat domestic with hot water or steam from a boiler thru the coil. (Heat-Flo 316 Stainless Steel Indirect Water Heater Tank with single heat exchanger 80 Gallon - HF-80)
Any help here would be appreciated.
Am I thinking wrong here? Would this not be a simple design?