High density Nitrogen-Vacancy (NV) centre ensembles incorporated in plasma assisted CVD diamond are crucial to the development of more efficient sensing devices that use the properties of these luminescent defects. Achieving high NV doping with N2 as the dopant gas source during diamond growth is however plagued by the formation of macroscopic and point defects that quench luminescence. Moreover, such NVs are found to exhibit poor photostability under high laser powers. Although this effect can be harnessed to locally and durably switch off NV luminescence for data storage, it is usually undesirable for most applications. In this work the use of N2O as an alternative doping source is proposed. Much higher amounts of the doping gas can be added without significantly generating defects which allows the incorporation of perfectly photostable and higher density NV ensembles. This effect is believed to be related to the lower dissociation energy of the N2O molecule together with the beneficial effect of the presence of a low and controlled amount of oxygen near the growing surface.