I believe Norton Utilities used to have a pretty good startup disk-maker if you have that. Otherwise, try making a really pared-down system folder. Remove most of the extensions, fonts, etc. and it should fit on a floppy pretty well. I did it a couple of times when my LC II died and I don't recall having any problems.
I've never heard of disabling extensions rendering a disk unbootable, though. It sounds like it needs to be repaired to me.