Reference

Maintained reference material that supports the reviews: the office-suite comparison, the migration guide and the licensing cost model. Each page states its assumptions and the date it was last reviewed.

Office 365, Collabora and Proton compared. The same file in all three suites, everyday tasks tested, jurisdiction, encryption and per-seat cost side by side.
Moving off US software: the migration guide. Classify by consequence first, then six steps.
Licensing cost model. Compare per-seat licensing with every assumption stated.