I have been PE for on an off about a year and at the beginning it all went smooth, gained about 0.3inch with manual stretches, but the last 6 months I gained nothing and I actually injured my PF and ever since I keep reinjuring myself if I go ham on stretching(..I must cause I am not gaining). So I decided to look for an extender which would probably be safer for meatheads like me.

The issue:
I would like to purchase an extender but I don't know which one would be the right pick for my size. Please comment your suggestion and or recommendation, I have been searching for a while and I would really appreciate some knowledge from you guys.
My stats are 16.5cm/6.5inch BEG and 13.5cm/5.3inch Flaccid base girth.