Howzit volks!

My 60 bus has three bench seats (the cab's, and two facing seats
with a missing table in the middle, camper-style) that have been
reupholstered but need it done again, for comfort's sake.

My primary question concerns the underlying springs.
Should I remove the original springs entirely and simply
replace with foam or should I leave the springs in tact?
I'm fairly the sure the springs are original, at least they
feel that way.  

I'm planning to use one of the seat backs
as a bridge for the middle space (its already built for 
easy removal) in order to construct a bed.  Next question,
should I use the same types of foam for the bed seats as
I do for the cab seat?  What would be the most comfortable
setup for passenger long rides / sleeping on the bed?

Lastly, this is primarily a surf/camp mobile for SoCal so
what recommendations would you all give for the material?
I'm thinking of going with a heavy duty woven fabric
all around.  I would like the result to maintain a stock
look and feel, would this be achieved by vinyl only?

Many kudos in advance for any responses I receive.
Stay cool,

Danny D.
'60 bus