If you can turn up a decent pair of seats then recolouring to match the original interior and "topping up" the colour of everything else isn't too bad a job, either as a DIY or paying someone. Fulvia seats are really good seats. I had them as my "every day" option when I had an Aurelia with a bench seat that never went in and a pair of buckets for competition, one of which became my eldest son's gaming chair.
My vote is give yourself a month or so to hunt for better seats while sitting on cushions, bits of camping mat cut to size or whatever it takes to make it comfortable in the interim.
I'm also a fan of loose covers. More a 50s thing than 70s. The Aurelia bench had a lovely loose cover with map pockets on the back. These days you see it more "as the dogs make such a mess". Growing up it was towels over the seats to stop us sticking to them. Not sure I can quite visualise it for a 70s Fulvia but "a bad idea in the hope it sparks a good one".
Another idea is repaired seats. There are more and more "patina" cars now. Maybe replace the front seat bolsters but not the middles? (assuming that's the wear rather than all the stitching has rotted). That rather depends on you finding someone local who's interested in doing that as repairs of anything are always a right pain relative to a fresh start. My godson found (and pursuaded) someone to do a tricky torneau cover for his MG midget who usually does high end neon interiors for funky camper vans but was up for it.
Period buckets...again "a look" and if you go for it and follow through then why not? Bumpers off, driving lights, reversing light, map light, map nets, pen clip, trip meter, watch holder, navigators foot rest, harnesses.
Another way to go is a random pair of seats from an MX5 or whatever else...with heaters...but coloured to match everything else.
