I've been designing for a while and I seem to enjoy making web designs and iOS designs yet at the same time I feel like they aren't complete without the UX side yes making the UI is aesthetic and all but is it functional? If I made it for a business would it help them convert more sales that to me is the a very big gap in what makes design good.

So my question is what are some very good UX books or anything that I can learn from?

Thank you so much in advance!