I love helping people horse shop! All the fun & none of the pressure :P I'm 5'7" and 68kg (~149lb) and I don't feel comfortable on anything less than a TRUE 16.2hh. Lots of sellers/horse owners don't actually measure their horses and just estimate the size, thinking that they know well enough or that is what someone has told them. I have found lots of people say/think their horse is bigger than what it is, which makes it hard when you are looking at pictures. I'm sure you know and like the above post has said it really does depend on the horse. I would prefer something 17hh
But I ride english and like big horses. There is no good us telling you you need a 16.2hh horse if you are going to be intimidated by it on the ground.
A friend of mine just got a new horse and he is 15.2 but he is sooo muscley and walks around with his head in the air all the time, so it feels like your leading a 17hh horse. Another friend of mine has a 16.3 boy and he's such a sweety that it feels like your dealing with a 14.3hh hand horse :)
Good luck with your search, let us know how you progress so I can be excited for you