Your bladder never ceases to amaze me. I would have stopped at least twice on the way back from Croatia
I have a pee a few times on a 6hr flight, sure. I use the little (330ml) plastic Tropicana juice bottles; they are perfect for the job and have no value so can be chucked away afterwards.
I would never fly without a few of those bottles within reach
It would be stupid to do so and I totally fail to understand people who use the need to wee to dictate their landings. A landing is a hassle (Customs, PPR, PNR) and one burns a load of fuel climbing back up again. Due to variable refuelling etc delays one often cannot file the advance flight plan in advance, so one has to mess around with that too. All just to have a pee....
Same goes for oxygen, avgas, etc
I also thought it was possible to fly the airways in France as long as you maintained VMC
They are not airways in the UK sense which in the UK is Class A and prohibited to VFR. It is Class E airspace, which is open to VFR. But it has high bases - usually FL065, which means one can get stuck above cloud if the destination is totally overcast.