If you are considering going to a LSD , well most likely there is no LSD available for your transmission.
The Speed3 LSD wont fit the 5spd but should work on the 6 spd but not on Sky transmissions.
If it is it will set you back at least $1500 for the part unless you find a used on ebay.
Traction Concept has a kit to convert your oem transmission differential to a LSD .
https://www.tractionconcepts.com/2012-Mazda-3-GX-G35M-R-5-Speed-Manual-LSD-Kit-p/tcxmz3740.htm
This one was custom made for me and for the 5spd G35M-R manual transmission should also work for the G5M transmissions.
If your model is not listed ask. They may have already custom made it (have the specs) and have not listed it on their website.
Custom would require you have the transmission dismantled and able to photograph the diff and measure gaps between the gears.