Hi Wendy,
The difference a memory foam mattress topper makes is remarkable. The seating in lounges has to be firmer, due to the constant use it gets, which is why so many people find them too firm for sleeping on.
The subject of memory foam has been raised on this forum several times and many of us, especially those with bad backs, recommend memory foam toppers. An uncomfortable nights sleep is not what you want when you are on holiday.
We bought ours from Raskelf, one of the market leaders, who will even cut memory foam to shape for fixed bed caravan owners. If you tell them the model and year of your caravan, they have a catalogue of all the bed sizes. For ease of storage, we bought two, one for each parallel seat, and put them together when making up the bed as a double. They were rolled up and stored under the seats during the day. Obviously, in a fixed bed 'van they remain on the bed.
Good quality mattress toppers are fairly expensive, but how do you put a price on a good nights sleep? If you spread the cost over how many comfortable nights sleep you will have over the years, they are worth every penny.
The memory foam comes encased in a quality zip cover too. If anyone buying a memory foam mattress if heavily built, they advise you to go for the thickest density foam.