Three questions about zonesleep topper for upper bed

[RedCali]

Hi everyone, wondering whether to buy zonesleep, we find Cali upper mattress perfectly comfy,
just rather hot.
A double zonesleep is £180 and a Cali one is £237.50 with discount - apart from the fact that the double one is a bit wider, can anyone see a problem with using one?
If just rolled up, about how much space does a Cali zonesleep take up?
Do you put anything on the zonesleep to keep it clean, eg a duvet cover?
Thank you very much ,
Alison.