This is likely to be much more difficult than you'd hope.
Having replaced the electric steering unit on the Panda earlier this year, I have been close to the wheel and column. The column has a master spline, so the wheel will only fit one way. It is likely that all recent Fiats have a master spline. I did not of course measure the diameter of the column, so there is no data for comparison.
Beneath the wheel is the clock spring. This wonderful little housing takes the electrical connections to the wheel, for horn, airbag and radio buttons. Different for those with/without radio buttons.
To remove the wheel, the battery has to be disconnected and left 10 minutes or so to prevent the airbag triggering. Then three very fiddly clips have to be released. Having fought and sworn, sorry, not willing to remove just to measure.
To move your enquiry on will require you to do the work.
Diameter of shaft at splines.
Number of splines. Master spline is effectively two splines width. (Need to confirm)
Length of splines.
Length of thread beyond splines.
Connector type for clock spring.
Distance between base of wheel and clock spring, and column shrouds.
With all that, and I may have missed something, you'd then need to view a potential wheel, or hope someone with one is willing to do the same analysis.
Similar age wheels are likely to be compatible, as Fiat are likely to be consistent with connections and fittings, so a Punto wheel will probably fit. (Just a guess) Heavier cars are likely to have a bigger diameter column.
Older cars, such as the X1/9 did not have an airbag, and were not CanBus, so even if the wheel fitted, you'd have no airbag, and a permanent warning light on. Horn may also be a problem.
I achieved a nicer wheel by having it leather covered. Sent it away while the steering was being done. Takes a week or two, so an alternative vehicle is useful. See the last post on this thread:
https://www.fiatforum.com/bravo/351579-royal-steering-wheels.html