When I got the van it had three seat covers layered one on the next. Taking them off revealed the reason - the driver's seat foam had fallen apart on the side, presumably due to the driver sliding out again and again.
Enquiries at a panel beater pointed me to an upholsterer who did a great job as you see here. Interestingly they make the seat from scratch, sculpting foam and sewing the cover. It cost $385 but given how important it is to have a comfortable seat for long drives I think it's worth it.