Hello @Raffaele_Morelli sorry to miss your question.
I would recommend reading through the Installation and Setup page here https://github.com/openenergymonitor/HeatpumpMonitor/blob/master/installation.md it details all the different sensor options for the heatpump monitor board, you only need the MBUS kit if you intend to read from a compatible MBUS based heat meter.
If do not want to measure heat output from the heatpump, or dont have a suitable heat meter installed that you could connect our board up to then another option is to just measure the electricity consumption of the heatpump and flow and return temperatures to get a good idea of how the heat pump is working. You can do this with an EmonTx with either an ESP8266 adapter or an EmonBase which is a pre-assembled option rather than the heat pump monitor which is a kit that you need to assemble yourself.
You may be interested in this blog post by John Cantor exploring some of the things you can learn from both approaches https://heatpumps.co.uk/2015/09/09/heat-pump-performance-monitoring-examples/
