the general consensus on NS is to get skis 10cm too long for you. but i'd say if you go with at least a 170 to be safe and don't hit above the mid 170's.
somthin' like a 172 or so would be good. trust me its not to big. Im 170 cms tall and weight 124. but I still use the rossi scratch FS 174 in the park. most say thats too big. but don't get a really small ski!