Whats happeneing when the string is breaking? Is it always in the same spot? The easy-difficult answer is "Just dont hit it so hard", but you might have developed a burr somewhere if its breaking one string in the same spot all the time. Easy enough to fix that with a gentle filing.
By bottom E, I'm assuming you mean High E furthest from you in playing position? Some people like a heavier gauge string so they can really hit hard as they play, its harder to bend but you might get used to it.
An alternative is using just a heavier gauge string for your High E, if thats what your having trouble with. The majority of your bending will probably happen on G and B, so its easy enough to just double up your fingers for assisting bends on the outside E. I'd couple that with a fatter low E too and it'll give the sonic impression of a bigger string set across to board.