I don't really know how breast forms feel as I have never tried them, but I have great big boobs with implants in them and I don't really feel them unless I'm jumping up and down or something.
Funny thing though, when I first got my implants I bumped them into all sorts of things all the time. Especially doors and such. We humans don't usually notice but we actually clear objects at very close distance when we move around, and when the shape of our bodies change abruptly it takes time for us to adjust.