Cold air settles to the bottom and forces warm air to rise. Radiation sends heat to the skin through the air. Convection moves heat from one location to the skin by moving air. Moving air is called a breeze or draft depending upon how fast it moves. These facts govern human comfort.
You will be downstairs most of the day. A heat pump moves air over the skin in the winter time at about 85F or less. As the skin temperature is about 91F, there is always a sensation of a cool draft, so the heat pump resident usually wears a sweater or turns the thermostat up to 76F to compensate for the wind chill factor of the constantly moving air. Heat pumps are satisfactory for large public buildings, but less acceptable for homes. the heat pump offers 50% savings over straight electric heat, but is more expensive than fuel combustion heating appliances.
The best way to heat and cool your home will be to place the air conditioning in the location that will do the most good. Warm air from dwonstairs will rise upstairs. The cold air from upstairs will fall downstairs. Place and air conditioning blower in the attic to provide cooling to the upstairs rooms. Run a duct downstairs to cool the living room. The contractor can add a hot water coil to the upstairs blower coil unit to provide heat from the boiler water. You will be able to remove all the radiators from the upstairs rooms and use the heat from the hot water coil in the blower to heat the upstairs rooms.
You can then remove all the radiators from the downstairs to replace them with cast iron baseboard radiation. The radiation will provide the sensation of warmth you are accustomed to from your standing radiators without a draft. You will be able to keep your thermostat at 68F to feel warm. You will not have the fan noise downstairs.
If the contractor uses large ductwork and registers with a quiet blower, the fan sound will be slight upstairs.
As an alternative, the contractor can install the air conditioning upstairs as a separate item to bu used in the summer months and replace all the radiators with baseboard so no sound is heard.
These are hard-learned facts over 40 years as contractor, Director of Education for Fedders, and Director of Education for heating and air conditioning manufacturers. You can learn more about hot water heating at http://www.hydronic.net