Any map will do you.
It's very easy to get around manhattan. We walked an awful lot, and only took the subway a couple of times. The street system is very simple - Avenues 1-11 running up and down, and Streets run from across (e.g. you are on the junction of 7th and 42nd and you want to get to the Empire State which iirc is on 5th and 35th, you go down 7 streets and across 2 avenues). The distances involved are not huge, but bring good walking shoes as you will end up doing a lot of walking.
Downtown and the financial district is a bit different, but it's small enough that you can't get too lost.