Being oversized and walking any distance in wet jeans is going to be painful.
Not only do they get heavy when wet and take ages to dry out, the seams will rub you raw.
Even for dry use if your overweight then the seams are going to be uncomfortable after a while walking.
I put on a fair bit of weight a few years ago and found most of the hiking trousers i used to wear to be uncomfortable between the groin area down to my thighs, i've since lost a lot of the extra weight and those same trousers are now comfortable again.
Couple of options for you as i see it.
1/ Look around for some trousers that have the seam that isn't in-between your legs
Pretty much every half decent hiking brand make hiking trousers, no idea what sort of sizes they go up to, but if you're struggling to find European brands that fit try so brands that are made for the American market as their sizes tend to be bigger.
2/ Buy some longer cycling type shorts to wear under your jeans, again shorts that have no seam or at best have a flat seam.
My advice is to go for #1 as there is no advantage to hiking in jeans and only many disadvantages.
They might make good work trousers but the material is not good for cold wet days out hiking in the UK.