When I started Airbnb I had a full size futon bed with a good quality innerspring futon mattress, but still it was a futon. I upgraded to an acutal full size bed on a bedframe after a few months. Since then I’ve upgraded again to a Nest Bedding Mattress. In those upgrades I stuck with a full instead of a queen because it’s a small room. I could fit a queen but queen sheets also cost more. However I could also use the new sheets on the Airbnb bed and then start using them on my bed when they got old.
In the 400+ guests I have not had a single complaint, per se, about the bed. A few people have said a queen would be better. But at <$50 a night I’m not upgrading for just a couple of people. The fact that the bed is extremely comfortable makes a difference more than the size.
In your situation I would upgrade to a queen if it fits in the space and get a well-reviewed mattress. I’m sending you a PM.