After you found out that your building does not have too much specific heat losses and would be suitable for installing heat pump, you must consider what type of heat pump to install and how powerful should it be.
For choosing a type of heat pump you must first decide what will be the source of energy. I would recommend deciding according to the following sequence. If you have a plenty of land space around your house, at least double or triple of house quadrature, I would recommend installing horizontal collector based heat pump. If you have underground water sources I would recommend to install ground water based heat pump – in that case you must drill two wells 20 – 50 meters deep to reach underground water. If you don’t have neither a lot of space around your house, neither underground water, I would recommend installing vertical geo-collector based heat pump as I did. This option is expensive but very reliable; you must drill one or two wells from 60 to 150 meters. In case none of above options suits your situation, then I would recommend installing air sourced heat pump that is using outdoor air as source of energy. This is the cheapest solution, but also less effective in comparison to others. I would not recommend installing outdoor air sourced heat pump if winter temperatures frequently drops under -5 degrees Celsius.
To be on a safe side I would recommend making few calculations before deciding. Find an engineer and decide together. Maybe you would be able to decide what type of heat pump to choose, but you will definitely need help when deciding how powerful the heat pump should be and how much of energy resources it will require – there are a lot of factors to be considered (type of heating, winter temperatures, specific heat loss, peak winter temperatures…).