I spent last night in DS6 bed, he was camping in his brothers room and I was escaping DH's snoring. Couldn't believe how shit his mattress was, thin, noisy and I felt like I could feel the springs, I'm actually feeling quite guilty that I didn't noticed before. Probably not quite as bad for him as for me due to considerable weight difference but still!
I'm not sure whether a topper would help much, I've seen one for £75 with good reviews at JL, or if I just need to buy a new mattress. His bed is a single divan so could be in it for quite a while although we have been thinking about whether to get him a cabin bed (which I'm guessing would be a single).