Yes you can use a regular mattress in your RV if you want too instead of the RV Mattress.
I took the RV Mattress out of our RV and replaced it with a good mattress which is the same as I use at home and all I had to do was make a few adjustments to the bed frame in the RV to allow the regular mattress to fit into the space.
A regular mattress and an RV mattress are almost the same thing however the difference mainly is in the size and how they're made to fit into the space.
RV Mattresses are usually a few inches shorter or narrower than a regular mattress of the same size you'd use in your home.
The RV Mattresses are usually a bit more flexible so they move around easily in the RV when bringing it into the RV.
If you do not like the RV Mattress then you can replace the RV Mattress with your favorite regular mattress although you might have to make a few adjustments to the area where the mattress fits in.
But you don't have to keep the RV Mattress in the RV if you don't like it and can change the Mattress out to one you like instead.