(Grumbles) Used to be much tougher back in my days (I think I did it for the first time, also as a F2P guy, back in Naxx), with the old rank system (see below), but congratulations anyway!
https://hearthstone.wiki.gg/wiki/Ranked
https://hearthstone.wiki.gg/wiki/Ranked/2013-2020
So, apparently, it used to be 5 stars per rank from 5, which is the equivalent of current D5, to legend, now it’s only three.