The champions programme point is huge. In the smaller businesses I work with (10 to 200 people), you don't need a formal programme. You just need to find the one or two people who are already curious about Teams and give them permission to experiment.
What I've found is that adoption in SMEs fails for a different reason than in enterprise. It's not lack of training or executive sponsorship. It's that nobody sat down and said "here's how we're going to use these tools." Staff get given M365 licences and then left to figure it out. Six months later, half the team is on email, half is on chat, files are in three different places, and everyone's frustrated.
The fix is surprisingly simple. Agree as a team where conversations go, where files live, and how tasks get tracked. Write it down on one page. Make it visible. That agreement is worth more than any training course because it removes the daily "where should I put this?" decisions that drain people.