I bought this memory foam topper. If you use search terms including “campervan” it seems to double the price, but this fits a 120cm RIB perfectly and was only £50. I put the mattress from the SCA pop on first, then the memory foam and sleep well, despite being a fussy sleeper.

RECCI Memory Foam Cooling Mattress Topper Small Double Pressure Relief 120x190x5 | eBay
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