Hi and welcome on your first post.
As you can imagine this question has been covered many many times. Try a quick search as honestly there are to many to post.
In brief there are many options but nothing can be left up top other than the original mattress.
Only option I know and have done myself is to replace the standard mattress with a thinner 1" one and add a zonesleep.
Both of these are available from the club shop and with a discount if you are a VIP member which gives you discount to the shop and many others. It's s no brainer option if you buy stuff for your Cali.
https://vwcaliforniaclub.com/shop/p...ty-replacment-upstairs-mattress-use-zonesleep
Mike
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