Minimum width of adult bunks/bench? Cushion/mattress width?

Not sure what to do here... thought you might help.
My 6'x10' trailer has two 5' E-tracks running along both walls from the side door back to the rear doors. One is just under the windows at about 46" height and the other is about 20" off the ground. Originally I was going to have stacked bunks using the E-track stud brackets running wall-to-wall, but I didn't allow enough room between the E-tracks (with the width of the studs, etc.) So up until now I've had one bunk, 36" wide and 69" long at 46" above the floor, against the back of the trailer. It's a 1/2" hardwood ply surface resting on three 2x4s held up by six beam sockets.
I want to add another bunk/bench, also the width of the trailer (69"), on the lower E-track. I have 20" of width left to work with. I can leave this 20" wide, which would probably make a great seat, but I'm sure it's too narrow to sleep on. So I should cut the 36" upper bunk back a bit, yes? What the's minimum reasonable width for a sleeping bunk for an adult? I could split the difference and make both bunks 28" but then both would be too narrow, yes?
Once the measurements are set, I'm going to order those cushions/foam. Is 4" thick too thick, just right or not enough? Would I be better served with 3" thick cushions? I know they compress some when you sit/lay on them.
What do you think? Thanks. -Gary
My 6'x10' trailer has two 5' E-tracks running along both walls from the side door back to the rear doors. One is just under the windows at about 46" height and the other is about 20" off the ground. Originally I was going to have stacked bunks using the E-track stud brackets running wall-to-wall, but I didn't allow enough room between the E-tracks (with the width of the studs, etc.) So up until now I've had one bunk, 36" wide and 69" long at 46" above the floor, against the back of the trailer. It's a 1/2" hardwood ply surface resting on three 2x4s held up by six beam sockets.
I want to add another bunk/bench, also the width of the trailer (69"), on the lower E-track. I have 20" of width left to work with. I can leave this 20" wide, which would probably make a great seat, but I'm sure it's too narrow to sleep on. So I should cut the 36" upper bunk back a bit, yes? What the's minimum reasonable width for a sleeping bunk for an adult? I could split the difference and make both bunks 28" but then both would be too narrow, yes?
Once the measurements are set, I'm going to order those cushions/foam. Is 4" thick too thick, just right or not enough? Would I be better served with 3" thick cushions? I know they compress some when you sit/lay on them.
What do you think? Thanks. -Gary