I know some people down here who ride Belgian draft horses for fun, and
they use one of those "extra stirrups" -- I've seen them advertised in
horse magazines, it's a small fillis-type stirrup on a thin leather strap
that you tie to your saddle -- it drops below your regular stirrup so you
can climb up, like a ladder, then you pull it up and tie it on the
saddle, out of the way. One female rider is not even 5' tall and she
uses this to mount that Belgian -- you should see it!!
Glenda & Lakota (no extra stirrups needed for me!)