Tire pressure and types of tires

The tire pressure that Michelin and Citroën advise is way to low. At such a low pressure the 2CV tends to drift if you go fast around corners. The tires squeak and you will drift.
That's why we use 2.0 bar (29 PSI) on all wheels. The tires wear less and the driving behavior is much better.
It is legal to drive on 125SR15 or 135SR15 tires. The standard tire is 125SR15 and you won't have advantages in using 135SR15. So it depends mainly on the availability and the price, which tires to choose.

Snow tires are not necessary if you only have snow for a few days every winter. The 2CV behaves very good on snow anyway. Because of the front wheel drive, the short distance between the axles and the small tires you have a big advantage over most other cars.
Snow chains can help to get you quickly out of a mess. If you have to drive under snowy conditions for a longer period of time every winter snow tires are recommended.