My cushions were ready to be replaced when I bought the boat so I had them made thicker and with slightly denser foam. No 'bottoming out' for me, anymore!
On my previous boat (John - you may remember I had a 28' Sundancer), everything was still in nice shape, but we wanted more cushioning. I bought a memory foam topper, cut it to size and it made a world of difference. That Sundancer's berth was very wide - even though I bought a king size topper, I still had to cut two more, small triangular pieces for the two bottom corners of the berth. The Offshore isn't nearly as a wide - take your widest point and compare that measurement to the width of a queen or king size topper. Truth is, though, you don't really have to cover the extreme bottom/side corners since no body part really touches there, anyways.
Make a template from plastic or paper. Lay the foam out in your house and trace the template. Cut it with... an electric turkey knife! Hands down, the easiest thing to cut it with! Although we kept the bed made pretty much all the time in the Dancer, when I didn't want it all set up, I would roll the foam up kinda like a sleeping bag and run a rope around it. It actually got pretty small and tight.