I got myself a new middle seat off ebay for a £10... you should find one on ebay or here, people take them out and put cubby boxes in.
Then I got an exmoor trim kit for the two front seats... new foam seats and backs included AND covers, including head rest covers to match the middle seat I got.
When I say covers these are not cheap and tacky... good stuff. I think I paid about £130 in April.
I stripped the old seats.... but take note of how the covers come off and keep plastic studs and wire supports. I took pics to remind me... and it helped.
I wire brushed the frames and gave them a coat of Hammerite making sure I did not over paint them and they could still be adjusted.
Fitting the new foams and covers was okay.... but you do need 2 people to stretch the covers tight and secure them. I used a staple gun to cover the head rests, just fold the cover neat... the head rest frame has a wood base. Take the head rests out when you have the seats out. Put the seat on the floor and use a foot to wedge it, just pull the head rest and wiggle it off. No catches...it just pulls out.
The main problem I had was getting the seats out... what a tw*t of a job. The bolts are likely to be very tight and I snapped 1.... so use lots of lub.
Sure the guys on here will be able to suggest seats from other vehicle that fit, are cheaper and more comfortable.