Loving Caravanning life but...

I don't know where you live, but the Aldi near me has single memory foam toppers in stock. I was looking for a double, but they had none. If you have a Poundstretcher near by, they have all sizes in and are very reasonable.

You don't say what your van is. If you did maybe some could offer specific advice.  

Ps I think our local Aldi still had a couple of memory foam toppers in last time I looked

We have done the memory foam toppers for years but due to the amount of storage space they need we went for a Vango self inflating mattress last year, best purchase we have ever made bedding wise.

 Agree with self inflating mats. If duvalay memory foam isn't enough then I doubt the Aldi version will be better. 

Have you tried both sides of the mattress, one side might be harder / softer than the other?

Maybe you have one of the thinner Duvalay mattresses? The Gold (5 cm) version is extremely comfortable and when used on top of a normal caravan or Motorhome seat should be more than adequate. 

you say that ypu have chosen these sleeping arrangements 'for now'.

what other sleeping accommodation do you have in your layout van?

You may need to replace the foam in the cushions. We use regal Furnishings in Ilkeston, but there are several firms that would do it for you. It made a huge difference to us.

hi I have a Romahome camper and the sofa isn't very thick ,so bought a luxury mattress topper from Argos it's 5cm and as my sofa is so narrow fold it in half ,then added a 2.5 cm one from poundstretcher they sell them all the time as do B&M and also look up on the internet you can get mattress toppers made to measure 

You attribute your back problems to sleeping on the sofa cushions. Like you, we use our sofas as two singles.  I also suffer with low back pain, but I found the activity of putting on the sheet and tucking it in the killer for me, rather than sleeping on the cushion.  In fact, I sleep better in the van than at home.  My solution was to put on a quilted mattress cover and fitted sheet on the first night, then leave it on during the day with a throw over the top, and replace the back rest cushions.  Yes, there's still a bit of cushion moving to do but, otherwise, it's just a case of stowing the pillow and duvet under the bed in the morning, and getting it our again at night.  Might be woth a try?