Any third party or worse sellers are never a place to buy bike parts unless beyond desperate and some how in the middle of nowhere and there is no bike shops anywhere nearby and things have gone south. However Kool Stop bought from authorized sellers are a great option. You can get a full size version of that poster from their website so you can double check easily and your local shop can likely order them for you if they don't already carry them. I prefer stocking their stuff personally because it is good quality from a good company who cares about quality and also cares about their customers and their owner or President Tim is just a super sweet guy who does a lot of charity as well on his own.

In terms of thickness stick with what the manufacturer recommends but generally that is more on the rotor side pads aren't usually super different because there is only so much space between pads and rotor. It is not like cable rim brakes where you can go a little thicker and adjust a bit and make it work.