Yes metallic paint is very expensive - looks great though. I think the comfort mattress is worth having (esp if you can get it thrown in!) to level the seat contours and make a flat bed, but I agree with
@dspuk - you're likely to want something on top of that too, especially if you sleep on your side.
The sea to summit fits the bottom bed perfectly, and could be used on top of the comfort mattress. In my view you would not need the comfort mattress in addition, but might allow the S2S to be less inflated if you like a softer bed.
The S2S also fits the upper bed of course (that bed is slightly wider), and again, can replace that mattress and be left in the top deflated (note others' concerns above). It is much more comfortable than the VW mattress.
I would take £130 for the S2S. I'm in London if you wanted to pick up, or I could get a price for postage - probably under £10.
I can recommend joining this forum - its a gold mine. We can then message each other directly.