You will not see any parachute manufacturer tell you, "if you weigh X, you should buy Y size of parachute". They all offer sizing charts which will show you the trade-off of descent rate vs opening time for various weights placed upon their chutes. They let the pilot decide which range they are comfortable with. If you fly close to terrain more often (ie the mountains), opening time may be more important to you. If you fly more in the flatlands, descent rate may be of more importance.
Keep in mind that NO parachute claims to guarantee your safety, even if it does open as planned. I have heard one manufacture say a successfully deployed parachute just gives you something nice to look at as you plummet to your death....a bit dark but it shows that there are no guarantees in this sport!
Here is a great article from WillsWing about parachute care and usage