I wear the Levis 541s and can say that they definitely are a nice fit. However, what's important to note is that not all the 541s are stretchy. The really dark wash 541s do NOT stretch like the lighter washes as they seem to be made of a different material and are noticeably thicker, probably to help hold in the dark dyes better. As a result, you need to stick to the lighter washes.The ones I told BlueBadger about are Levis, the 541 style.
As an example, the color "Rigid Dragon" does not stretch. I had to return that pair.
I can confirm that the colors "Midnight" and "Lake Merrit" do stretch.