It's actually not firm at all! Very squishy. You do sink in slightly. You wouldn't be worried about back issues with something made entirely of soft foam? FWIW it's very comfortable night after night and I don't run into any back pain, but I'm still young, so maybe that'll take time to manifest itself? Back issues are my main worry.
And yes, boats are generally more humid than most homes - especially when left alone, they get extremely humid.
And yes, I am Dutch, I guess you could tell by my username :) I'll have to check out a Hastens sometime.
If you side sleep, I don't think you'll run into too much trouble. To be sure, lay on your side and ask someone to check your spine is straight. Your hips should sink in a bit, but not too much.
Else, if you are a back or tummy sleeper and it's squishy, you should try to switch to something more firm.
If what I suggested is too radical, try natural latex, which is quite firm.
A good entry point to the (pretty lacking) sleep ergonomics literature is:
I actually sleep on my back. Not that I don't believe you, but why should I try something firmer when I find this mattress to be very comfortable and never feel back pain? I assume that this causes a risk of future back pain - would you have any information about that specifically?
And yes, boats are generally more humid than most homes - especially when left alone, they get extremely humid.
And yes, I am Dutch, I guess you could tell by my username :) I'll have to check out a Hastens sometime.