We wouldn't buy a mattress that has memory foam as a top layer but that is a personal preference. We did buy a Lucid latex 12" hybrid (steel springs and foam) mattress from Amazon. It was delivered rolled up in a box and was easy to drag through the trailer. Our 31 ft. fifth wheel has a full 60" x 80" queen. We have about fifteen nights on it and find we like it a lot.
Amazon seems to have mattress shopping dialed in a little. Most of the mattresses show a foam type profile and a firmness rating. There are also a number of good Youtube videos. I cross shopped at mattress stores and it became obvious to me their hybrid mattresses were made in the same factories as the online ones, except twice the cost.