What specific data were you looking for? When did you last check out OSM? (There's been a huge push on data completeness in recent years that is now bearing fruit)

Combining datasets: You'll have to check the terms of the license agreements. In general, for ODbL-licensed data (like OSM), if you generate a "derivative database" (e.g. by merging multiple datasets), you will have to release this derivative database under ODbL terms as well. This would essentially rule out commercial data.

One way companies avoid this is by segregating the datasets, e.g. use a commercial dataset for hotel data, and use OSM data for streets and non-hotel POIs, without ever combining them into a single database. (But you'll have to check with an IP lawyer to be certain about the correct way to implement this).