I had to make a drastic change in the plans for my truck bed, because no matter how hard I tried, the process of getting in and out of the bed was extremely difficult when it was raised up off the truck floor.
So, when faced with the decision of having storage space under the bed or ease and speed of ingress and egress I went with the two gress's and put the bed on the floor.
When I got the Styrofoam blocks under the bed to raise it up where I wanted it, giving me adequate storage space underneath, I put my inch and 1/2 thick mattress cover on the plywood and instantly discovered that it was no different than sleeping on a board. That told me that I was going to have to use the 4 inch thick foam to have any chance at a comfortable nights sleep.
After doing that it didn't take a genius to see that with a four-inch pad and my sleeping bag on top of that, I was going to have to become a contortionist to get into it, so for the sake of my poor bad back I decided to put the bed on the floor with just enough Styrofoam under it to level it up and find some other place to put the tons of camping gear that I carry.
After I got the bed leveled up on the floor and the four-inch foam pad on it, getting into it is now a piece of cake. I'm able to get into the bed quite easily from the passenger side door by just sitting down on the bed and scooting towards the back until my head is at the head of the bed. It's a little awkward trying to close the passenger door when I'm in the bed but its just a matter of me being in the right position, and getting used to it.
So I believe I have my truck bed in a usable condition now. I know I'll have to do some tweaking after I've slept in it a couple of nights but I feel that right now it's at least as comfortable as the cot I use in the tent.