Freestyle skiing actually covers different kinds of skiing. 3 categories in total:
Freestyle All-mountain skis
Freestyle Park skis
Freestyle Backcountry skis
These kinds of skis feature waist widths between 80 and 95mm and can ride switch (backwards) without a problem thanks to their twin-tip profile (front and tail tips). In order to make freestyle moves and pivots easier they often feature tip and tail rockers. This specific profile gives freestyle all-mountain skis an easy and playful personnality. The skis feel nimble and perform both in the park and off piste.
If you want something as versatile as can be we recommend a length between your height and 5cm under.
If you want something that's more park-oriented, prefer a shorter ski, 5 to 10cm under your height. Don't go any shorter or you will miss stability which is not something you want when you're landing a trick.
These are skis specifically designed for park shredding and street jibbing. Like FS all-mountain skis, park skis are twin tipped but they are narrower and don't always feature rockers. This helps increasing the effective edge length for added grip, which can come handy on the icy walls of the pipe. Park skis are often more technical and more demanding than FS all-mountain skis. Their flex is stiffer and they are primarily intended for advanced and expert skiers.
In order to choose the correct length you first need to define the use you're going to make of it:
Park & Pipe: Pick a ski at your height. You will get more stability on landings and more grip.
Jib and Street riding: Pick a ski that is slightly shorter than you (few centimeters). It will feel more nimble and more lively.
This is probably the most specific use of a freestyle ski. It requires a wide and playful ski that can send and land tricks on deep powder. FS BC skis come with waist widths over 100mm for optimal support on soft snow. Like every freestyle ski, FS backcountry skis are twin tipped and feature sometimes a light traditional camber and more often a flat camber or reverse camber. In order to enhance floatation, these skis are also equipped with two long rockers helping skiers keep the tips above powder surface.
In order to stay afloat, backcountry skis are longer than traditional freestyle skis. A ski that's 5 to 15cm taller than you is about right.