Hi i havent been here on for some time now like years ha ha we have converted a vv van to our first camper we desperately need a used drivers seat thats the only thing thats wrong the springs are shot.
I replaced the seats in a different but similarly common van from abreakers yard. Is it springs or foam that has gone? If the latter re-upholster is a possibility. If it's an older variant it may be hard to find one with good foam. If the fabric is ok you can get new foams from ebay. Our breakers yard seats were upgrades - better fabric, armrests & 2 singles instead of a passenger 'bench' - but the drivers NS bolster was still collapsed so I fitted a new foam base insert. The fabric was bonded to the foam but easy to remove in chunks & scrape off. I think Vivaro is same.
Dunno if this is for your variant
https://www.ebay.co.uk/itm/Seat-Cushion-Foam-Padding-Seating-Car-Vauxhall-Vivaro-Trafic-New/142034556693?hash=item2111eb5715:g:RFEAAOSwmAZe6FFr
Aye - I reckon it will be. The springs, such that they are, are normally just a kind of steel wire arrangement under the foam. Vivaro likely the same. You'll be taking that off to fit the foam insert.