Bit of memory foam, take very little, can change anything into a pretty comfy sleeping area. We've had a big sheet on our 181g bed for 4 years now and it's been perfect for us that way.
Also since you're going to get the chance to look inside some Pods, do just that, really spend some time in the models that you have available on the lot. Sit in them, imagine yourself stuck inside one during a long wet rainy trip, imagine where you'd be comfortable.
That's the more important thing I try to advise all of our new owners on, is to spend as much time as you can in them before picking your model. The right Pod for you will be the one where when you're sitting in the different areas or even laying in the bed you feel the most comfortable.