my niv deck was very control oriented, and i ran a heavy counter package bc at the place i play at niv is just one of those generals that draws you immediate hate as soon as ppl see who your general is. so without changing your deck too much, id recommend to limit the card draw to just yourself.Blue Sun's Zenith
and Recurring Insight
are two card draws you might think about adding. Mind Over Matter
quickly became my favorite card in my niv deck, can hold off angry opponents quite well. Teferi's Puzzle Box
makes games interesting and also gives you a steady way to draw cards if niv is out. those are my suggestions, as i said my deck was a good bit more control oriented than yous appears, but i think these cards could help you. good luck man, have fun with it.