We had not problem with using standard sheets on the bed in our 24D. The Murphy bed is the easiest for both of us to have a roomy bed and each of us able to get up during the night without crawling over the other person. The "twin" beds are 32" wide for 6 inches narrower than a standard twin which is why we passed on this when looking at RV's.
Don't overlook the dry bath in the layout and the room in front of the toilet. In the Navion 24D it is less than 13 inches from the edge of the toilet seat to the wall and this is one significant defect with the design. A six foot tall person is going to have to sit side saddle on it.
In retrospect the 24D or any of the Winnebago class C RVs that use the Sprinter cab chassis are not a good choice for towing or for boondocking between the low GCWR and very low OCCC and the DC only fridge along with the electric induction burner and having only a single propane burner.