Have you checked with Gander Mountain or Bass Pro shops for safety harness?
If you're able to sit still and scent down really well I say 12' - 18' is perfect a lot of others may say to go a lot higher but when you begin to go above the 18' range you're entering into the natural umbrella of the woods and limiting your viewable range. I believe it's better to see your hunting area as best you can but If you go too high with your treestand you're going to miss some action. Good Luck
If you're able to sit still and scent down really well I say 12' - 18' is perfect a lot of others may say to go a lot higher but when you begin to go above the 18' range you're entering into the natural umbrella of the woods and limiting your viewable range. I believe it's better to see your hunting area as best you can but If you go too high with your treestand you're going to miss some action. Good Luck