sheepskin's porous = bad. latex isn't = good.
you need to try a bunch of different brands/types, like the magnum. Anything that says extra thin is generally smaller i think. one size doesn't fit all... if it's too small and you have to stretch it too much to put it on then
a) it hurts
b) it's hard to roll all the way down and
c) it actually comes off easier. Usually inside. And then she freaks, "oh god don't tell me it's still inside" yadda yadda yadda
d) easier to last longer
practice... so you can throw it on in a second in the dark.
nothing's better in the act than a little piece of mind, and you won't be freaking for a week afterwards.