Vanessa upstairs foam mattress

[LTW]

I replaced the VW comfort mattress with the Vanessa 10cm memory foam topped mattress last year and it's made a big difference to our sleep. I'm now considering the Vanessa upstairs 6cm memory foam topped mattress and was wondering whether anyone can recommend this option. The website mentions removing the VW foam and placing the new foam mattress inside the existing cover. My two questions are whether the existing cover will fit considering the VW foam mattress is only 4cm deep and will the roof close with a 6cm mattress in place. Any help appreciated.