To get under the falls you have to climb at least for a small part of the way.
You can climb the fall and not get wet by climbing the safe wooden stairs that are right next to the falls. There are many platforms along the stairs that are great for viewing and taking pictures
I guess you could find a guide who would meet you along the stairs where you could enter the falls for a quick dip into the water
I climbed the falls 20 yrs ago off of a cruise. I remember the cruise folks saying the water "only comes up to your knees" and that it was an "easy" climb. The water seemed higher and, at times, gushed over my head. I remember watching a lot of older (and I don't mean "old") folks having real troubles. Hey, it wasn't easy for me and I was young and in great shape.
It's not super hard but, once you start, you kind of have to finish. And, if you're not in reasonably good shape, it could be somewhat tough. I strongly recommend wearing tennis/athletic shoes or beach shoes. They obviously will get totally soaked but going barefoot -- if it's still an option -- is painful and, as noted, the rocks are slippery.