You should be able to use an IDE-drive, or even better, a CF-card, if you can find an IDE-controller that fits.
Assumes that the machine is new enough that it knew how to deal with ST506 drives.
(The oldest machines needed to boot from floppy to load drivers for the ST506 controller)
This is because while IDE and ST506(MFM) are very different drives, the IDE-controller was designed to be functionally identical to the ST506.
To use a CF you also need an IDE-to-CF adapter, but they can be found cheaply on the net...