I have some type of Jeep seats in mine. They're adapted to the Astro bases with flatstock and some 3/8 hardware. They'renot the world's best seats, but they're far better than the worn out conversion seats it had prior. I did the same with some PT Cruiser seats, but the angle was wrong and they kept sliding me forward.
YUP. I just used appropriate fairly heavy gauge angle stock bolted to the the seat frame and then drilled to match the bolt pattern of the seat. Used all graded fasteners and since I had power adjusted seats everything still adjusts forward, backward, tilt etc.. I found a pair of Recaro AM19 seats all black and one had a small tear in the seat so I disassembled and took the cover to an upholstery shop to replace the torn panel. Since I had it apart, I reconditioned the seat cushions, put reinforcement fabric in the normal tear locations and installed seat heaters since they were all apart. So comfy now!
If yours are conversion van seats, you might want to try stock Astro/Safari seats from a junk yard. I think my 93 LT seats are very comfortable, especially for long drives (I've driven my Astro from Alabama to California several times). Any drivers seat you find will probably be badly worn, but you can swap the base onto a good passenger or 2nd row seat.
(sorry if a Captain Obvious comment)