Bandwidth of voltage divider with PMOS switch
This image should help you place the capacitances where they belong in the MOSFET model. You need all three and they should all be listed in the datasheet.
Personally though, I probably wouldn't bother with the MOSFET parasitic capacitances in this case.

https://micro.rohm.com/en/techweb/knowledge/si/s-si/03-s-si/4873
https://micro.rohm.com/en/techweb/upload/2017/03/si_2-2_capf.gif