Hi Andy and welcome to our forum. I think, from what you're describing, it's going to be very difficult for anyone to give you a diagnosis here on the forum unless this is exactly something they have experience of. However I thought I'd just send you a message of support to try to buck your spirits up! I'm going through a somewhat similar experience just now with my older boy's Punto 1.4 8 valve.
He went on holiday and left the car with me to look over whilst he was away (I'm a retired mechanic but my hay days were long ago) with particular emphasis on the clutch which only works when the pedal is nearly on the floor. I was about 75% sure it was a master cylinder problem so got stuck in doing a major service and general check over during which I found a few faults - like cooling (radiator) electric fan only working on high speed. All in all a good couple of days work (at my geriatric rate of working) Then, with everything else attended to I tried to change the clutch master cylinder only to find it's a job for a contortionist with at least 21 inch long fingers and double jointed elbows. Not realizing that the pedal box really needs to come out I gave up and handed the job over to our local Fiat independent who made a lovely, but not particularly cheap, job of it. I was gutted to find no change in the clutch action! I asked the garage's opinion (and several people on the forum offered opinions too) and the consensus seemed to be probably there was a problem with the clutch itself. So, ok, they took the box out for me (at 73 this sort of physically demanding activity is just slightly beyond me these days) The clutch was very worn. Only a few thousand miles left on the driven plate and deeply grooved on the ends of the diaphragm fingers. I got them to fit a new clutch (3 piece Valeo kit) and they power bled the hydraulics. It was deeply depressing to then find that, although the clutch action was much lighter - you would expect this with a new clutch having been fitted - the pedal action really hasn't changed. It's still very nearly on the floor before it "frees". Really the only things we haven't yet changed are the flexible hose - which I've today checked for swelling under pressure - and the slave cylinder. The garage are convinced it's the slave and one has been ordered which should be here for Thursday/Friday. So the car should be all fixed and ready for my boy to take it back at the weekend. He should be starting a new job soon and the car will be fundamental to his success as it has some "antisocial" shift hours.
So what started out as a "simple" service and sorting out of a few problems has ended up with "Dad" being considerably out of pocket and still not knowing if I'm maybe going to have to lend him my car (I hate lending my car to anyone) until the mystery of the clutch is resolved - At least the heavy work on the clutch is done and I'm sure the problem is now in the hydraulics so I can mess about with this myself without laying out any more cash! I'm slightly comforted by the fact that, although not totally "goosed", the clutch itself was well worn and not that much longer for this world so we would likely have been needing to do it in the next year which might have impacted on his job.
It occurs to me to ask where you live (not actual address of course)? It might be that one of the more knowledgeable Forum members is near you and could have a listen and offer you an opinion?
So there you are. In the words of the old saying "Life's a B***H (and then you die). - I've been cheered up immensely by my younger boy and his wife presenting us with a new grandson just 2 days ago. I spent yesterday afternoon comforting and cuddling him with the help of their wee daughter, whilst my Mrs and daughter-in-law were sorting out bedding and crib and - - -. Put everything into perspective really!
Kindest regards
Jock