It would be great to be able to switch between profiles too so I can flip between “Work” and “Home” and it would change my bookmarks etc on the fly.

Not possible for Sync to have two different sets of bookmarks, or any data for that matter.

Separate Firefox Profiles on each device, along with separate Sync accounts would do what you want. No limit on the number of Sync accounts for each user, but a separate email address is needed for each Sync account.