Can't PC floppy drives write double density? You'd think they could, having been encumbered with a compulsion for backwards-compatibility ever since RISC processors came out. (Not that I'm the one to talk, whining about Apple dropping AppleTalk from 10.4 to 10.5 and PPC in 10.6)
You could also try a zip drive, if you can find a cheap one for both the Mac (SCSI) and the PC (how did they connect zip drives back in the day?), handy storage instead of having to keep track of a stack of DD floppies. But if you can't find these items for cheap, get a second old Mac, one with Ethernet and a SuperDrive to use as a compatibility layer (though you can use it for all kinds of fun stuff).
You could also try a zip drive, if you can find a cheap one for both the Mac (SCSI) and the PC (how did they connect zip drives back in the day?), handy storage instead of having to keep track of a stack of DD floppies. But if you can't find these items for cheap, get a second old Mac, one with Ethernet and a SuperDrive to use as a compatibility layer (though you can use it for all kinds of fun stuff).