I'm sorry to say that none of them are very comfortable, even the ones with the name brand mattresses. They have to stay relatively thin in order to fit into the sofa. You might try a memory foam mattress topper or perhaps newer sofa beds have these type of mattresses. Good luck!

We have owned a sleeper sofa where the matters was a Sealy. Quite thick and nearly as comfortable as my regular (firm) mattress. Unlike many sleeper sofas, you do not feel the frame/mechanism of the sofa itself.