I always use the Dakine Proform straps.
They run about $21 a piece, and I've had good luck with them. They are adjustable, so you can use them with shoes or barefoot.
As far as install, I install them just before the incline area in the footwell. The way to measure this, IMO, is to get someone to hold the strap, and stand on the ski in the jumping position, which, for me, is having the natural bend where my toes all connect to my foot right on the bend of footwell.
Then, I mount the strap just before the middle of the top of my foot.
As dumb as it may sound, this is a VERY important placement (depending on your riding style).
I ride surf alot, and the first ski I mounted foot straps on I didn't totally think it through like this. My ski had the the very thin 3M type skateboard tape on it, with no under padding (which is great and not great all at the same time). At the time, I thought strapping the foot almost flat would be best for wave jumping, but even though that position was great for maneuvering the ski around and jumping it, it was the WORST possible position for landing the ski.
That's just my opinion. I'm ready to install my 4th set this coming week.