I found that I had to go up one size in jeans to allow for a diaper but that going up two sizes worked better to conceal a very wet Dry 24/7 diaper with a booster pad. If you looked at me you might think that I have a big bottom but you would not think "diaper."
The shape of the jeans is as important as the size in order to find an acceptable fit and achieve good concealment. I wear Levi's 559 jeans with a Dry 24/7 diaper with a booster pad and plastic pants. The diaper is not noticeable.
Levi 550's can hide about any diaper combination you could think of, including day-weight cloth diapers, but are noticeably more baggy.
I also go up two sizes in Dockers.
Don't forget the old adage - "It's better to bulge than to leak."
--John