You can reduce the number of bottom solid layers if you want the decrease the floor thickness. Another option is to increase the number of perimeter outlines. That will make the software prefer perimeters vs solid layers.
However, if you have something like 6 bottom solid layers and only 2 perimeter outlines, the software WILL add these solid sections on steep overhangs. It has to, otherwise you wouldn't be respecting the number of bottom solid layers that you requested.
If you have tried decreasing the bottom solid layers, and increasing the number of perimeters, and neither worked, you can create a second process for the overhang section of your model so that you can use different settings for it:
https://www.simplify3d.com/support/tuto ... f-a-model/