This is just excellent and newly available: Mass in C, by the famed director and dedicated champion of sacred music Richard Terry. It is in unison and extremely easy but also dignified and fitting in every way. I'm thinking here of new EF Masses that have been established that new to get going fast with an easy Mass. This would do it. Of course it is also suitable for the OF.
The person who transcribed this Mass is Oliver Hayes, who also has a wonderful CPDL page here.