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As long as outside air temp is higher than ground water temp you might get from the well, air/water heat pump is more economical than water/water (using a well or plowed circuit).
We installed water/water geothermal heat pump 7 years ago and never looked back (170m well). Ours is on-off type but new pumps have VFD drive so they are able to "throttle" compressor somewhat. (at low loads they still do on-off regulation though).
Usually, modern heat pumps have electrical immersion heaters as "backup". Our pump is able to produce ~8kW of heat by compressor alone. But if something happens to compressor or it runs out of capacity, 9kW electric heater kicks in in three steps.
So far, resistive heater was never needed. House stays warm in -4F using nothing but heat pump (whose compressor draws 1.4kW of electricity, rest is "uplifted" from the well).