Recommendation for a 22 cm deep mattress for a study bed?

I'm getting a StudyBed next week, a small double and need a mattress.
I'm 5 ft 7 woman and weigh 10 to 11 stone. I'm used to have a Jensen bed but my partner and I are light sleepers so, for the last seven years or so, I've been sleeping on the sofa, taking the Jensen topper with me.
I've bought Hypnia memory foam mattresses for my parents and my partner (who ended up preferring the firmness to the Jensen) but I like to turn and sleep on my stomach. I still find the Hypnia memory foam mattress still can cause me to wake up during the night from a sore hip or shoulder, though for just £160 it's amazing value.
When I go on holiday I take a photo of the mattress if I'm impressed. I loved the Sealy Beautyrest mattress at the London Hotel in West Hollywood, and the Mybed (so boutique) mattresses at the Sofitel chain. I also loved the Swiss Schwob bed.
However, the Studybed will only accommodate a 22 cm deep mattress. With the StudyBed costing around £2500, I think it's worthwhile - at the age of 48 - to invest in a decent mattress for myself.
Please advise.
Thank you