For RT2012 one of the ways around having to have expensive solar solutions is to fit a thermodynamic boiler.
This one on Mano Mano is 1.5k euros and may be what we need.
According to one green energy
This comes on the list under ventilation…
This might be one? https://www.atlantic-climatisation-ventilation.fr/ventilation/chauffe-eau-thermodynamique-sur-air-extrait/aquacosy-av/aquacosy-av-100l-et-200l