I have crossed the Alps several times at different times of the year. I go by the GAFOR routes in Switzerland, or if clear by direct route. The GAFOR routes are given in Jeppesen and will give you the flight planning routes and the weather on those routes can be got from
www.meteoschweiz.ch, and follow the business and internal flights to get to the GAFOR wx.
The swiss met system is very good.
Have you flown in the mountains before? If you are new to mountains I suggest that you look for the lowest routes on the nicest day. Wind can be very tricky!
It's really beautiful and satisfying. St Gallen is a good place to stop for fuel. There is a mountain radio frequency 130.35, but check that it hasn't changed.