We have the Lycksele Murbo sofa bed combination. I still think the "mattress" is extremely hard and uncomfortable. So, I bought a memory foam topper from costco ("full bed" size). It cost me about $120. WELL worth it! My mother in law was visiting over the summer for a month, so I wanted her to be comfy. She slept like a baby on the bed with the topper. When she was ready to go home, I rolled up the topper and put it back in its box, until next time.
For one or two nights, I think most people would find it pretty comfortable. However, I sleep on a Tempurpedic bed and extremely firm beds aggravate my back/neck and lead to migraines. I also get sore hips. I lay down on the sofa occasionally, and my hips get sore. I do like it for sitting up and reading, though. Lots of good support and the back is at a nice high level (reaches up just past my shoulders). I use a Poang footstool with the sofa and it's the perfect height.
I would suggest buying the cheapest mattress Ikea offers, and then splurging on a memory foam topper for it when guests will be using it long term.
My favorite thing about this is how easy it is to set up as a bed. Also, I love the removable (WASHABLE) cover. Worth its weight in gold!