hello!

I'm the same height as you, new to mountain biking (well all cycling) too, and my mountain bike is the Specialized Hardrock Sport Disc. which I have in the 15.5 frame size. If you look at the sizing guide, I think this frame size is suggested for up to about 5ft 7. I adore it, the bike just feels a perfect size and so much fun. I found that this was a better fit for me than the equivalent Myka. It's worth trying a Myka too, or similar, in case you're more comfortable with the shorter handlebar.