Advice on how to not over cook my steak
I would suggest two options, but first, when taking the temperature of a steak, insert the probe through the side of the steak. Aim halfway up, and have the end of the probe as close to the center as possible. The probe should be level, rather than angled.  This might allow you to be more accurate.  You don't need to take the temp at several places...just the center.

The first option, is called the "reverse sear" method.  This works well for steaks of about an inch in thickness or greater.  Preheat your oven to 275F (135C). Place a rack on an oven tray.  Season the steaks well.  Place on the rack, and put into the preheated oven.  Cook until your desired doneness...maybe 125F to 135F  (52C - 57C). At the low oven temp, this will probably take at least 45 minutes, but this depends on thickness. Remove from the oven and rest for 15 minutes. Sear in a screaming hot cast iron pan for 1 minute per side.  Slice and serve.  

Alternately, you can use sous vide to cook the steak perfectly.  This has been addressed here before.  Basically, you heat water to the desired internal temperature of your steak.  Place the steak in a zip lock bag, submerge in the water for an hour (the water temp must be maintained over the entire period, preferably with circulation).  Remove, pat dry, season, and sear as above.  Slice and serve.  ...poking your steak with a thermometer is not necessary with this approach.