I have boxes of both 5.25 & 3.5" diskettes including most DOS Versions since DOS 1.1. You can use a program like WinImage
to make images of the old diskettes and the images can be read by VMs just like an ISO.
I have an old machine that has 5.25 & 3.5" floppy drives in it that allows me to copy stuff from one format to the other.
I have a VM on my machine with DOS 6.22 which is fun to play with but for most times when DOS is needed or wanted, DosBox works well.
As far as old software, I have original disks of Lotus 1-2-3 and also have a copy of VisiCalc somewhere.