It seems there is nothing astronomically intuitive to use as a mass unit between the kilogram and lunar mass.
A Giza's pyramid worth of mass? A teaspoon of neutron star matter mass? These simply do not work.
An intermediate solution may be telling the app to show the magnitude with the "nearest" unit, so it shows for example 8.52 X 10^18 kg as 0.0000712 lunar masses (I don't know, it's an example).
If a new mass unit it's going to be added, I'd stick to giga/tera/petagram (or at least Mkg, Gkg...), altough they're not very intuitive, they're standard.