My best advice, owning a vacation rental with a queen-sized sofa bed is to buy a quality bed with a good pull-out system where the support bar is not right under the body of the sleeper and with either a latex or memory foam mattress. The density of the foam, at least the underlayment layer of the mattress, is important for the sleeper to not feel any of the bars.

Look for a sofa bed that can accommodate the thickest possible mattress. Most can handle a 4" or 5" mattress thickness and it's really hard to have a comfortable night on the 4" thickness, regardless of type of mattress. Obviously, a 6" thick or thicker mattress is going to provide a better sleep. There are some sofa beds out there that will accommodate 8" and I've even read, 10" mattresses, but they were well out of my budget. I ended up buying from the Sleepers in Seattle online store and have been very satisfied with their customer service and the quality of the sofa bed. They advertise here on Houzz, so I'm not going outside of the "family" with this recommendation.

In my case, even though the sofa bed was quality, I "cheaped" out and opted for the basic included mattress. This was a coil mattress that was maybe 4" thick with really cheap springs and compressed down to nothing when slept on. It also broke down very quickly and I replaced it with a 5" thick coil mattress. 5" was the thickest mattress I could put in the sofa bed because any thicker and the mechanism would not close properly or if forced, might bend and/or break.

The 5" coil mattress, an Englander Mattress company sofa bed mattress provided a better sleep, but still not a great sleep.

I ended up buying a very affordable (less than $200) 5" memory foam mattress from a large online-only retailer with free two-day shipping (who would that be?) and have had great reviews on the sleep quality ever since.

If this mattress were for me, rather than in a rental, I would have bought a quality latex mattress. However, ease of opening and closing of a sofa bed is a consideration for a vacation rental and the memory foam mattress weighs a lot less than a latex mattress would.

For the record, my vacation rental is rented for 42 out of 52 weekends a year, so it gets reasonably heavy use. I hope my non-professional, non-expert experience is helpful and good luck with your decision.