Pop top foam mattress recommendation please

[rollercoaster]

We have a pop top that did not come with a mattress,
not sure but I could guess theres not a lot of space up there,
so its crucial to find (buy) a thin but comfortable mattress.
One idea is to go to a pop top seller and try the options,
but I thought to ask on here what people think.
I usually sleep on the Dunlopillo latex foam at home,
and dont really like "memory foam" type of beds,
I feel they just squash up too easily, not tried many tbh.
So thats it really, recommendations, reviews, ideas welcome.
Thanks.