I don't have your pituitary issues but slept on the sole for every passage
to SoPac and back. Wife got the the leeward berth. I used a camping mat and really had no issues with being comfortable. Actually, the motion of the boat is less and easier to cope with down that low. Just be sure that the boat you get has a deep sump to trap any water
that gets below. You don't want to sleep in sloshing water
which you will in a modern sumpless boat.
Still, you'll spend more time at anchor
so will want some berth that will fit you. Probably any boat will need to be modified if you want a berth you can stretch out in.