Hi Cecelulu,
Welcome to our matress forum :).
Thanks for the post, and sorry about the back pain. This situation is interesting because any changes made could throw off your husbands nice fit with this mattress.
Backs can be very complex and it can take some analysis and detective work and some educated guesswork to track down the cause of back discomfort or pain. The most important goal of a suitable mattress is to support the spine and joints in neutral alignment in all your sleeping positions so that the muscles and other tissues can fully relax and not work during the night to maintain good alignment. It also needs enough softness on the surface to allow your pressure points to sink in enough so that direct pressure on various parts of the body don’t cause soreness. Too much firmness or too much softness in either the comfort or support layers can both lead to alignment and pressure issues, discomfort, or pain in various areas of the body.
I think you should maybe look at a plush latex topper, Talalay 19 or 24 ild in probably only 2 inches thick, it may be just enough and also not too much to throw off your husband’s sleep style.
Hope this helps, you can read more about this in this back pain post.
Thanks,
Sensei