Pycroft
You have had some excellent advice and info in this thread. I would echo what Sir Niall Demented cautions you about.
It is rare on any long trip in this part of the world to get consistant CAVOK all the way. I presume you have little or no instrument training other than the appreciation bit you got in the PPL.
I have flown trips where it has been beautiful weather only to find thick fog lying over the channel infact I took some unusual pictures of ships funnels carving a line in the fog tops
Route close to airfields and dont be afraid to divert if your not happy.
As Sir Niall said dont allow yourself to be put under any pressure and explain this to your passenger.
Having said all that I remember being in your boat many moons ago when I too flew my first solo into Europe.
I had relied on the watchful eye of an experienced friend pilot for previous trips until this one day the two Pax turned up to be followed by a phone call from the friend to say he had crashed his car on the way to the airport.
The two PAX where keen to go leaving me on my own with a lot of trepidation. it was the best thing I did
So have fun but do watch the weather and if at all doubtful dont go.
Pace