This was the first time since owning Apple Watch that I did a full phone setup as new. Prior to that I always did iTunes backup/restore because I was worried about losing activity/fitness data.
This time I did iCloud backup first (no more iTunes backups yay). Made sure health data was going to iCloud.
Setup phone as new, let iCloud stuff come back down (for Notes/Messages/Health, etc).
Unpaired watch from old phone, paired to new phone. Downside is that I lost 5 hours of stands and about 80 active calories of burn, so I had to stay up extra late getting stands haha... not sure why the backup wasn't more recent than the 5 hours but it did get my yoga workout from earlier that morning at least.