You could absolutely boot a stripped-down Mac OS 8 on a floppy, including the beige G3. Apple even provided them ("Disk Tools").
Apple even still hosts a download of the Disk Tools floppy for MacOS 8.1! https://download.info.apple.com/Apple_Support_Area/Apple_Sof...
Fascinatingly, the System file on the Disk Tools 8.1 floppy is actually a build of System 7, with HFS+ support grafted on.
https://github.com/elliotnunn/HFSPlusBackport/blob/master/re...