Improving bed comfort

Burtspieeater

 We have recently bought a 4 yr old  2 berth caravan which appears to have had very little use.

 We did originally intend to buy a new fixed bed caravan but found that the length of beds available to be only borderline acceptable. This and other issues led us to a rethink and we are now the very happy owners of a Compass Corona 462.

 The bed size is great but we would like to improve the comfort of the bed. My wife thinks it is too firm whilst  I am concerned that we may soon develop sagging by always sleeping in the same spot. 

One idea I have is to purchase a self inflating double mat as used in camping, this would I hope overcome both of our concerns.

 Has anyone else tried this?