Replying to First Time Ski Swap

So, I'm new to skiing in general and will be heading to the annual ski swap in my town to pick up my gear. I've been to my shop and done some reading online. Im a BEGINNING skiier, im located in Montana so what im looking for in the skis is just something surfy and floaty for the deep powder but can also do a little bit of park. I'm 19 years old, 5'8"tall and weigh about 135lbs.

I hope this is enough information. I just not sure what sizes I can go between really, especially with the fact that the rocker means you need to get a different length just has me a bit puzzled.

I've been debating make a thread like this all week, and finally went through with it, because i know there are tons already. So thank you for your help..