You're right about the wheels. They weren't too bad 10 years ago, but nowadays they look lost. It's quite a slab-sided car as it is, with fairly huge rear wings and the little 16" wheels don't help.
19" wheels will fit, and 235mm wide tyres have been fitted with 18" wheels, though the excess of traction starts to take it's toll on the drive train as the usual clutch-protection mechanism is a bit of wheelspin.
225/40 on 18" wheels is common and safe. 19" wheels might be better kept to 215/35 or 225/35 at most, as 235/35R19 is getting rather larger than the standard rolling radius.
If they're going to rub, they'll do it on the rear wheel arches, and at the fronts on steering lock.
I fully support the idea of new, bigger wheels, but I'd recommend no more than 8.0 wide wheels, that you stick to the standard offset, and wouldn't personally go higher than 225mm width.
If it were me too, I'd probably (actually, I did) stick to 18" and go for a design which isn't too fussy and avoid deep-dish looks. Spokes which go all the way to the rim make the wheel look bigger. Deep dish looking wheels always look small.
I had a friend who had a Cougar on 19s. He had 215/35R19 tyres. It looked great, but to be brutally honest it was barely tolerable, and I was much younger and more up-for-it at the time. While the Cougar handles very well for a FWD car, it's ride quality was never a strong point. Even on the standard wheels it has a fidgety, lumpy ride at low speed round towns etc. On 19s, it'll knock your fillings out...
Just my 2p.
Have a look in out Pictures section. There are loads of photos of various wheels and sizes on the car. Personally I think the car suits fairly simple, elegant designs but other people have different views on what looks good.