You need snowboard specific laces. They are stronger and have a good flex.
Around 90 inches or a bit more is a good length.
I bought some from this site and they are awesome!!!!!!! Plus they have different colors so you can customize your look and give your boots a new look.
P.S. keep your boards edge off the laces. LOL
Oooh, they come in pretty colors!
I replaced the laces on my boots the night before a trip. It was probably much harder than you'd ever have it, since I got some custom ones that had metal ends and I had to squish the metal ends with pliers to get them to fit through the first few holes (for some reason, those were very narrow compared to the rest). Anyway, pliers and a lot of pulling and I now have more durable laces on my boots.
Also, yeah, keep your board edge off your boots/laces while on the lift. That took me a while to get (I still use my foot to lift it up at the beginning), and that's how my first set of laces got shredded.