To me there is no way to avoid the uniboob thing. Binders have to press stuff down. You can learn yourself to adjust in a different way (by example down and out, or up and out, or just down/ to the sides). I heard some people like to wear a compression shirt under it, so that it fits tighter (which may prevent uniboobage).
To your itching question;
Also I like to use the baby powder with menthol in it, because menthol relieves itching/ or potato starch (it clumps less). But that is just how I do it.