For our 170A we bought a 3" memory foam mattress topper and cut it to fit the beds. Looked like it would be really comfortable, but it compresses more than expected and isn't as comfortable as we had hoped.
Let us know if you come up with a better solution.
I’m blessed as I like my mattress hard enough to to bounce a nickel lol. So for us no additional cover is needed. But I would recommend a good bed topper that should provided more comfortable sleeping.
My 2012 ERA 170 rear seat folded down to a bed ends up with the seat back portion on a different level than the seat bottom portion.
I put a 2 inch thick foam pad on the seat bottom portion to "level it up" and put a two inch foam pad over the entire bed to smooth and level it.
My wife and I sleep "with the seat" (side to side) and it's as comfortable as our home bed.