If you don't mind the car not being all original, you might consider some racing seats.
I bought a pair that were on sale at a local automotive supply shop and dropped them in my Alfetta GT and I love them.
I created templates for the rails, drilled holes in the new seat rails and had them bolted in, in under two hours.
The Alfetta body did not allow for the end adjustment handles, so be aware of width limitations before you buy any if you choose to do so.
They sit an inch lower so now I have more head room. I'm 6 feet tall.
They are similar to these.
My son was seriously considering a pair of Sparco or other reclining seats for his '86 before he decided to redo the OEM Recaros. We looked at several different manufacturers, and we did find that you have to be careful about clearance on the inboard side, with the driveshaft tunnel. Watch the overall width of the new seats, measure carefully and if you can, try to find some examples on display at speed shops so you can actually test fit them. We did that with his car when we removed the passenger seat, drove our Alfas to a couple of stores where they had display seats, and set them in there. Took some time and gas but it was worth it.
The Recaros, if they're repadded and the foam contoured correctly, can be very comfortable. He had a simplified upholstery pattern done though, instead of the multiple rolls as on the originals.
Miata seats fit about anything, and fiero's if you're looking for junkyard seats. Lots of '80's bmw's in junkyards but they're probably in bad a shape as your gtv6.
New seats, I've used carbeau recliners that fit it all alfas, and are relatively cheap. Carbeau also sells the direct fit seat mounts.
You can also do a "seats wanted" on the bb and get used seats from other gtvg and milanos that that fit. I found an alfa Milano good front and rear seat set in St Louis for $200 and was a direct fit into my 78 alfa sports sedan.
You want to put true Recaros in there! Real comfort, performance, and lumbar support.
I put a pair of LS-C (same as a Milano Verde) in my GTV6 for dual-purpose use. They bolt right in if you drill one extra hole in the seat rail (takes about 5 minutes) and remove the inboard side seat recliner knob (one phillips screw). It's narrow in the GTV6. I'm not sure if the standard Milano seats fit in there from a Gold/Silver but they too are much higher quality seats than the standard GTV6 fare.
It's funny 91Spider mentioned Miata seats - I was very close to adapting a set till I landed the NOS Verde seats. I wanted the speakers in the headrests! The seat is much more durable than the GTV6 original seat and they even have a tan color that was reasonably close to the GTV6. Also cheap and readily available.