'Woman' is singular, 'Women' is plural. I keep seeing time & again, looking for a genuine women. Ok it might be the case that you are looking for more than one woman, so in this case, women would be right, but then leave the 'a' out because you can't be looking for 'a women'.
I have to point out that this isn't just the guys I'm talking about. I often see on a ladies profile..... 'I'm a genuine women'!!
You are a WOMAN, not WOMEN. - oh unless you have a multiple personality disorder maybe?